Tempo ramps - rename meter_at() -> meter_at_frame() & make the ticker slightly more...
[ardour.git] / libs / ardour / tempo.cc
index fec74ccfe0341bb6989762b3b69b8a942c71a17b..36ac3a8203d03703ffccb8b2a001615d3eec14d5 100644 (file)
@@ -73,14 +73,20 @@ Meter::frames_per_bar (const Tempo& tempo, framecnt_t sr) const
 const string TempoSection::xml_state_node_name = "Tempo";
 
 TempoSection::TempoSection (const XMLNode& node)
-       : MetricSection (0.0), Tempo (TempoMap::default_tempo())
+       : MetricSection (0.0, 0, MusicTime)
+       , Tempo (TempoMap::default_tempo())
+       , _c_func (0.0)
+       , _active (true)
+       , _locked_to_meter (false)
 {
-       const XMLProperty *prop;
+       XMLProperty const * prop;
        LocaleGuard lg;
        BBT_Time bbt;
        double pulse;
        uint32_t frame;
 
+       _legacy_bbt = BBT_Time (0, 0, 0);
+
        if ((prop = node.property ("start")) != 0) {
                if (sscanf (prop->value().c_str(), "%" PRIu32 "|%" PRIu32 "|%" PRIu32,
                            &bbt.bars,
@@ -89,20 +95,18 @@ TempoSection::TempoSection (const XMLNode& node)
                        /* legacy session - start used to be in bbt*/
                        _legacy_bbt = bbt;
                        pulse = -1.0;
-                       set_pulse (pulse);
+                       info << _("Legacy session detected. TempoSection XML node will be altered.") << endmsg;
                }
-       } else {
-               warning << _("TempoSection XML node has no \"start\" property") << endmsg;
        }
 
-
        if ((prop = node.property ("pulse")) != 0) {
-               if (sscanf (prop->value().c_str(), "%lf", &pulse) != 1 || pulse < 0.0) {
-                       error << _("TempoSection XML node has an illegal \"beat\" value") << endmsg;
-               } else {
-                       set_pulse (pulse);
+               if (sscanf (prop->value().c_str(), "%lf", &pulse) != 1) {
+                       error << _("TempoSection XML node has an illegal \"pulse\" value") << endmsg;
                }
        }
+
+       set_pulse (pulse);
+
        if ((prop = node.property ("frame")) != 0) {
                if (sscanf (prop->value().c_str(), "%" PRIu32, &frame) != 1) {
                        error << _("TempoSection XML node has an illegal \"frame\" value") << endmsg;
@@ -145,15 +149,6 @@ TempoSection::TempoSection (const XMLNode& node)
                set_active (string_is_affirmative (prop->value()));
        }
 
-       if ((prop = node.property ("bar-offset")) == 0) {
-               _bar_offset = -1.0;
-       } else {
-               if (sscanf (prop->value().c_str(), "%lf", &_bar_offset) != 1 || _bar_offset < 0.0) {
-                       error << _("TempoSection XML node has an illegal \"bar-offset\" value") << endmsg;
-                       throw failed_constructor();
-               }
-       }
-
        if ((prop = node.property ("tempo-type")) == 0) {
                _type = Constant;
        } else {
@@ -161,10 +156,20 @@ TempoSection::TempoSection (const XMLNode& node)
        }
 
        if ((prop = node.property ("lock-style")) == 0) {
-               set_position_lock_style (MusicTime);
+               if (movable()) {
+                       set_position_lock_style (MusicTime);
+               } else {
+                       set_position_lock_style (AudioTime);
+               }
        } else {
                set_position_lock_style (PositionLockStyle (string_2_enum (prop->value(), position_lock_style())));
        }
+
+       if ((prop = node.property ("locked-to-meter")) == 0) {
+               set_locked_to_meter (false);
+       } else {
+               set_locked_to_meter (string_is_affirmative (prop->value()));
+       }
 }
 
 XMLNode&
@@ -182,28 +187,17 @@ TempoSection::get_state() const
        root->add_property ("beats-per-minute", buf);
        snprintf (buf, sizeof (buf), "%f", _note_type);
        root->add_property ("note-type", buf);
-       // snprintf (buf, sizeof (buf), "%f", _bar_offset);
-       // root->add_property ("bar-offset", buf);
        snprintf (buf, sizeof (buf), "%s", movable()?"yes":"no");
        root->add_property ("movable", buf);
        snprintf (buf, sizeof (buf), "%s", active()?"yes":"no");
        root->add_property ("active", buf);
        root->add_property ("tempo-type", enum_2_string (_type));
        root->add_property ("lock-style", enum_2_string (position_lock_style()));
+       root->add_property ("locked-to-meter", locked_to_meter()?"yes":"no");
 
        return *root;
 }
 
-void
-
-TempoSection::update_bar_offset_from_bbt (const Meter& m)
-{
-       _bar_offset = (pulse() * BBT_Time::ticks_per_beat) /
-               (m.divisions_per_bar() * BBT_Time::ticks_per_beat);
-
-       DEBUG_TRACE (DEBUG::TempoMath, string_compose ("Tempo set bar offset to %1 from %2 w/%3\n", _bar_offset, pulse(), m.divisions_per_bar()));
-}
-
 void
 TempoSection::set_type (Type type)
 {
@@ -216,7 +210,7 @@ double
 TempoSection::tempo_at_frame (const framepos_t& f, const framecnt_t& frame_rate) const
 {
 
-       if (_type == Constant) {
+       if (_type == Constant || _c_func == 0.0) {
                return pulses_per_minute();
        }
 
@@ -231,7 +225,7 @@ TempoSection::tempo_at_frame (const framepos_t& f, const framecnt_t& frame_rate)
 framepos_t
 TempoSection::frame_at_tempo (const double& ppm, const double& b, const framecnt_t& frame_rate) const
 {
-       if (_type == Constant) {
+       if (_type == Constant || _c_func == 0.0) {
                return ((b - pulse())  * frames_per_pulse (frame_rate))  + frame();
        }
 
@@ -243,7 +237,7 @@ double
 TempoSection::tempo_at_pulse (const double& p) const
 {
 
-       if (_type == Constant) {
+       if (_type == Constant || _c_func == 0.0) {
                return pulses_per_minute();
        }
        double const ppm = pulse_tempo_at_pulse (p - pulse());
@@ -257,11 +251,10 @@ TempoSection::tempo_at_pulse (const double& p) const
 double
 TempoSection::pulse_at_tempo (const double& ppm, const framepos_t& f, const framecnt_t& frame_rate) const
 {
-       if (_type == Constant) {
-               double const beats = ((f - frame()) / frames_per_pulse (frame_rate)) + pulse();
-               return  beats;
+       if (_type == Constant || _c_func == 0.0) {
+               double const pulses = ((f - frame()) / frames_per_pulse (frame_rate)) + pulse();
+               return  pulses;
        }
-
        return pulse_at_pulse_tempo (ppm) + pulse();
 }
 
@@ -272,7 +265,7 @@ TempoSection::pulse_at_tempo (const double& ppm, const framepos_t& f, const fram
 double
 TempoSection::pulse_at_frame (const framepos_t& f, const framecnt_t& frame_rate) const
 {
-       if (_type == Constant) {
+       if (_type == Constant || _c_func == 0.0) {
                return ((f - frame()) / frames_per_pulse (frame_rate)) + pulse();
        }
 
@@ -287,7 +280,7 @@ TempoSection::pulse_at_frame (const framepos_t& f, const framecnt_t& frame_rate)
 framepos_t
 TempoSection::frame_at_pulse (const double& p, const framecnt_t& frame_rate) const
 {
-       if (_type == Constant) {
+       if (_type == Constant || _c_func == 0.0) {
                return (framepos_t) floor ((p - pulse()) * frames_per_pulse (frame_rate)) + frame();
        }
 
@@ -323,7 +316,7 @@ The integral over t of our Tempo function (the beat function, which is the durat
 b(t) = T0(e^(ct) - 1) / c
 
 To find the time t at beat duration b, we use the inverse function of the beat function (the time function) which can be shown to be:
-t(b) = log((cb / T0) + 1) / c
+t(b) = log((c.b / T0) + 1) / c
 
 The time t at which Tempo T occurs is a as above:
 t(T) = log(T / T0) / c
@@ -343,6 +336,13 @@ t = b log (Ta / T0) / (T0 (e^(log (Ta / T0)) - 1))
 By substituting our expanded t as a in the c function above, our problem is reduced to:
 c = T0 (e^(log (Ta / T0)) - 1) / b
 
+Of course the word 'beat' has been left loosely defined above.
+In music, a beat is defined by the musical pulse (which comes from the tempo)
+and the meter in use at a particular time (how many  pulse divisions there are in one bar).
+It would be more accurate to substitute the work 'pulse' for 'beat' above.
+
+Anyway ...
+
 We can now store c for future time calculations.
 If the following tempo section (the one that defines c in conjunction with this one)
 is changed or moved, c is no longer valid.
@@ -370,7 +370,7 @@ double
 TempoSection::compute_c_func_pulse (const double& end_bpm, const double& end_pulse, const framecnt_t& frame_rate)
 {
        double const log_tempo_ratio = log (end_bpm / pulses_per_minute());
-       return pulses_per_minute() *  (exp (log_tempo_ratio) - 1) / (end_pulse - pulse());
+       return pulses_per_minute() *  (expm1 (log_tempo_ratio)) / (end_pulse - pulse());
 }
 
 /* compute the function constant from some later tempo section, given tempo (whole pulses/min.) and distance (in frames) from session origin */
@@ -380,30 +380,30 @@ TempoSection::compute_c_func_frame (const double& end_bpm, const framepos_t& end
        return c_func (end_bpm, frame_to_minute (end_frame - frame(), frame_rate));
 }
 
-framecnt_t
+framepos_t
 TempoSection::minute_to_frame (const double& time, const framecnt_t& frame_rate) const
 {
-       return (framecnt_t) floor ((time * 60.0 * frame_rate) + 0.5);
+       return (framepos_t) floor ((time * 60.0 * frame_rate) + 0.5);
 }
 
 double
-TempoSection::frame_to_minute (const framecnt_t& frame, const framecnt_t& frame_rate) const
+TempoSection::frame_to_minute (const framepos_t& frame, const framecnt_t& frame_rate) const
 {
        return (frame / (double) frame_rate) / 60.0;
 }
 
 /* position function */
 double
-TempoSection::a_func (double end_bpm, double c_func) const
+TempoSection::a_func (double end_ppm, double c_func) const
 {
-       return log (end_bpm / pulses_per_minute()) /  c_func;
+       return log (end_ppm / pulses_per_minute()) /  c_func;
 }
 
 /*function constant*/
 double
-TempoSection::c_func (double end_bpm, double end_time) const
+TempoSection::c_func (double end_ppm, double end_time) const
 {
-       return log (end_bpm / pulses_per_minute()) /  end_time;
+       return log (end_ppm / pulses_per_minute()) /  end_time;
 }
 
 /* tempo in ppm at time in minutes */
@@ -438,36 +438,14 @@ TempoSection::pulse_tempo_at_pulse (const double& pulse) const
 double
 TempoSection::pulse_at_time (const double& time) const
 {
-       return ((exp (_c_func * time)) - 1) * (pulses_per_minute() / _c_func);
+       return expm1 (_c_func * time) * (pulses_per_minute() / _c_func);
 }
 
 /* time in minutes at pulse */
 double
 TempoSection::time_at_pulse (const double& pulse) const
 {
-       return log (((_c_func * pulse) / pulses_per_minute()) + 1) / _c_func;
-}
-
-
-void
-TempoSection::update_bbt_time_from_bar_offset (const Meter& meter)
-{
-       double new_beat;
-
-       if (_bar_offset < 0.0) {
-               /* not set yet */
-               return;
-       }
-
-       new_beat = pulse();
-
-       double ticks = BBT_Time::ticks_per_beat * meter.divisions_per_bar() * _bar_offset;
-       new_beat = ticks / BBT_Time::ticks_per_beat;
-
-       DEBUG_TRACE (DEBUG::TempoMath, string_compose ("from bar offset %1 and dpb %2, ticks = %3->%4 beats = %5\n",
-                                                      _bar_offset, meter.divisions_per_bar(), ticks, new_beat, new_beat));
-
-       set_pulse (new_beat);
+       return log1p ((_c_func * pulse) / pulses_per_minute()) / _c_func;
 }
 
 /***********************************************************************/
@@ -475,12 +453,10 @@ TempoSection::update_bbt_time_from_bar_offset (const Meter& meter)
 const string MeterSection::xml_state_node_name = "Meter";
 
 MeterSection::MeterSection (const XMLNode& node)
-       : MetricSection (0.0), Meter (TempoMap::default_meter())
+       : MetricSection (0.0, 0, MusicTime), Meter (TempoMap::default_meter())
 {
        XMLProperty const * prop;
-       BBT_Time start;
        LocaleGuard lg;
-       const XMLProperty *prop;
        BBT_Time bbt;
        double pulse = 0.0;
        double beat = 0.0;
@@ -495,14 +471,13 @@ MeterSection::MeterSection (const XMLNode& node)
                        error << _("MeterSection XML node has an illegal \"start\" value") << endmsg;
                } else {
                        /* legacy session - start used to be in bbt*/
+                       info << _("Legacy session detected - MeterSection XML node will be altered.") << endmsg;
                        pulse = -1.0;
                }
-       } else {
-               error << _("MeterSection XML node has no \"start\" property") << endmsg;
        }
 
        if ((prop = node.property ("pulse")) != 0) {
-               if (sscanf (prop->value().c_str(), "%lf", &pulse) != 1 || pulse < 0.0) {
+               if (sscanf (prop->value().c_str(), "%lf", &pulse) != 1) {
                        error << _("MeterSection XML node has an illegal \"pulse\" value") << endmsg;
                }
        }
@@ -510,20 +485,20 @@ MeterSection::MeterSection (const XMLNode& node)
 
        if ((prop = node.property ("beat")) != 0) {
                if (sscanf (prop->value().c_str(), "%lf", &beat) != 1) {
-                       error << _("MeterSection XML node has an illegal \"beat\" vlue") << endmsg;
+                       error << _("MeterSection XML node has an illegal \"beat\" value") << endmsg;
                }
        }
 
        start.first = beat;
 
        if ((prop = node.property ("bbt")) == 0) {
-               error << _("MeterSection XML node has no \"bbt\" property") << endmsg;
+               warning << _("MeterSection XML node has no \"bbt\" property") << endmsg;
        } else if (sscanf (prop->value().c_str(), "%" PRIu32 "|%" PRIu32 "|%" PRIu32,
                    &bbt.bars,
                    &bbt.beats,
                    &bbt.ticks) < 3) {
                error << _("MeterSection XML node has an illegal \"bbt\" value") << endmsg;
-               //throw failed_constructor();
+               throw failed_constructor();
        }
 
        start.second = bbt;
@@ -559,19 +534,23 @@ MeterSection::MeterSection (const XMLNode& node)
                throw failed_constructor();
        }
 
-       if ((prop = node.property ("lock-style")) == 0) {
-               warning << _("MeterSection XML node has no \"lock-style\" property") << endmsg;
-               set_position_lock_style (MusicTime);
-       } else {
-               set_position_lock_style (PositionLockStyle (string_2_enum (prop->value(), position_lock_style())));
-       }
-
        if ((prop = node.property ("movable")) == 0) {
                error << _("MeterSection XML node has no \"movable\" property") << endmsg;
                throw failed_constructor();
        }
 
        set_movable (string_is_affirmative (prop->value()));
+
+       if ((prop = node.property ("lock-style")) == 0) {
+               warning << _("MeterSection XML node has no \"lock-style\" property") << endmsg;
+               if (movable()) {
+                       set_position_lock_style (MusicTime);
+               } else {
+                       set_position_lock_style (AudioTime);
+               }
+       } else {
+               set_position_lock_style (PositionLockStyle (string_2_enum (prop->value(), position_lock_style())));
+       }
 }
 
 XMLNode&
@@ -604,7 +583,55 @@ MeterSection::get_state() const
 }
 
 /***********************************************************************/
+/*
+  Tempo Map Overview
+
+  Tempo is the rate of the musical pulse.
+  Meters divide the pulses into measures and beats.
+
+  Note that Tempo::beats_per_minute() has nothing to do with musical beats.
+  It should rather be thought of as tempo note divisions per minute.
+
+  TempoSections, which are nice to think of in whole pulses per minute,
+  and MeterSecions which divide tempo pulses into measures (via divisions_per_bar)
+  and beats (via note_divisor) are used to form a tempo map.
+  TempoSections and MeterSections may be locked to either audio or music (position lock style).
+  We construct the tempo map by first using the frame or pulse position (depending on position lock style) of each tempo.
+  We then use this pulse/frame layout to find the beat & pulse or frame position of each meter (again depending on lock style).
+
+  Having done this, we can now find any one of tempo, beat, frame or pulse if a beat, frame, pulse or tempo is known.
+
+  With tepo sections potentially being ramped, meters provide a way of mapping beats to whole pulses without
+  referring to the tempo function(s) involved as the distance in whole pulses between a meter and a subsequent beat is
+  sb->beat() - meter->beat() / meter->note_divisor().
+  Because every meter falls on a known pulse, (derived from its bar), the rest is easy as the duration in pulses between
+  two meters is of course
+  (meater_b->bar - meter_a->bar) * meter_a->divisions_per_bar / meter_a->note_divisor.
+
+  Below, beat calculations are based on meter sections and all pulse and tempo calculations are based on tempo sections.
+  Beat to frame conversion of course requires the use of meter and tempo.
 
+  Remembering that ramped tempo sections interact, it is important to avoid referring to any other tempos when moving tempo sections,
+  Here, beats (meters) are used to determine the new pulse (see predict_tempo_position())
+
+  The first tempo and first meter are special. they must move together, and must be locked to audio.
+  Audio locked tempos which lie before the first meter are made inactive.
+  They will be re-activated if the first meter is again placed before them.
+
+  Both tempos and meters have a pulse position and a frame position.
+  Meters also have a beat position, which is always 0.0 for the first meter.
+
+  A tempo locked to music is locked to musical pulses.
+  A meter locked to music is locked to beats.
+
+  Recomputing the tempo map is the process where the 'missing' position
+  (tempo pulse or meter pulse & beat in the case of AudioTime, frame for MusicTime) is calculated.
+
+  It is important to keep the _metrics in an order that makes sense.
+  Because ramped MusicTime and AudioTime tempos can interact with each other,
+  reordering is frequent. Care must be taken to keep _metrics in a solved state.
+  Solved means ordered by frame or pulse with frame-accurate precision (see check_solved()).
+*/
 struct MetricSectionSorter {
     bool operator() (const MetricSection* a, const MetricSection* b) {
            return a->pulse() < b->pulse();
@@ -622,8 +649,8 @@ TempoMap::TempoMap (framecnt_t fr)
        _frame_rate = fr;
        BBT_Time start (1, 1, 0);
 
-       TempoSection *t = new TempoSection (0.0, _default_tempo.beats_per_minute(), _default_tempo.note_type(), TempoSection::Constant);
-       MeterSection *m = new MeterSection (0.0, 0.0, start, _default_meter.divisions_per_bar(), _default_meter.note_divisor());
+       TempoSection *t = new TempoSection (0.0, 0, _default_tempo.beats_per_minute(), _default_tempo.note_type(), TempoSection::Ramp, AudioTime);
+       MeterSection *m = new MeterSection (0.0, 0, 0.0, start, _default_meter.divisions_per_bar(), _default_meter.note_divisor(), AudioTime);
 
        t->set_movable (false);
        m->set_movable (false);
@@ -637,6 +664,12 @@ TempoMap::TempoMap (framecnt_t fr)
 
 TempoMap::~TempoMap ()
 {
+       Metrics::const_iterator d = _metrics.begin();
+       while (d != _metrics.end()) {
+               delete (*d);
+               ++d;
+       }
+       _metrics.clear();
 }
 
 void
@@ -667,6 +700,7 @@ TempoMap::remove_tempo_locked (const TempoSection& tempo)
                if (dynamic_cast<TempoSection*> (*i) != 0) {
                        if (tempo.frame() == (*i)->frame()) {
                                if ((*i)->movable()) {
+                                       delete (*i);
                                        _metrics.erase (i);
                                        return true;
                                }
@@ -697,14 +731,28 @@ TempoMap::remove_meter (const MeterSection& tempo, bool complete_operation)
 }
 
 bool
-TempoMap::remove_meter_locked (const MeterSection& tempo)
+TempoMap::remove_meter_locked (const MeterSection& meter)
 {
        Metrics::iterator i;
 
+       for (i = _metrics.begin(); i != _metrics.end(); ++i) {
+               TempoSection* t = 0;
+               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                       if (meter.frame() == (*i)->frame()) {
+                               if (t->locked_to_meter()) {
+                                       delete (*i);
+                                       _metrics.erase (i);
+                                       break;
+                               }
+                       }
+               }
+       }
+
        for (i = _metrics.begin(); i != _metrics.end(); ++i) {
                if (dynamic_cast<MeterSection*> (*i) != 0) {
-                       if (tempo.frame() == (*i)->frame()) {
+                       if (meter.frame() == (*i)->frame()) {
                                if ((*i)->movable()) {
+                                       delete (*i);
                                        _metrics.erase (i);
                                        return true;
                                }
@@ -724,14 +772,13 @@ TempoMap::do_insert (MetricSection* section)
         */
        MeterSection* m = 0;
        if ((m = dynamic_cast<MeterSection*>(section)) != 0) {
-               //assert (m->bbt().ticks == 0);
 
                if ((m->bbt().beats != 1) || (m->bbt().ticks != 0)) {
 
-                       pair<double, BBT_Time> corrected = make_pair (m->pulse(), m->bbt());
+                       pair<double, BBT_Time> corrected = make_pair (m->beat(), m->bbt());
                        corrected.second.beats = 1;
                        corrected.second.ticks = 0;
-                       corrected.first = bbt_to_beats_locked (_metrics, corrected.second);
+                       corrected.first = beat_at_bbt_locked (_metrics, corrected.second);
                        warning << string_compose (_("Meter changes can only be positioned on the first beat of a bar. Moving from %1 to %2"),
                                                   m->bbt(), corrected.second) << endmsg;
                        //m->set_pulse (corrected);
@@ -767,8 +814,13 @@ TempoMap::do_insert (MetricSection* section)
 
                                        *(dynamic_cast<Tempo*>(*i)) = *(dynamic_cast<Tempo*>(insert_tempo));
                                        (*i)->set_position_lock_style (AudioTime);
+                                       TempoSection* t;
+                                       if ((t = dynamic_cast<TempoSection*>(*i)) != 0) {
+                                               t->set_type (insert_tempo->type());
+                                       }
                                        need_add = false;
                                } else {
+                                       delete (*i);
                                        _metrics.erase (i);
                                }
                                break;
@@ -780,7 +832,7 @@ TempoMap::do_insert (MetricSection* section)
 
                        bool const ipm = insert_meter->position_lock_style() == MusicTime;
 
-                       if ((ipm && meter->pulse() == insert_meter->pulse()) || (!ipm && meter->frame() == insert_meter->frame())) {
+                       if ((ipm && meter->beat() == insert_meter->beat()) || (!ipm && meter->frame() == insert_meter->frame())) {
 
                                if (!meter->movable()) {
 
@@ -790,11 +842,11 @@ TempoMap::do_insert (MetricSection* section)
                                         */
 
                                        *(dynamic_cast<Meter*>(*i)) = *(dynamic_cast<Meter*>(insert_meter));
-                                       (*i)->set_position_lock_style (insert_meter->position_lock_style());
+                                       (*i)->set_position_lock_style (AudioTime);
                                        need_add = false;
                                } else {
+                                       delete (*i);
                                        _metrics.erase (i);
-
                                }
 
                                break;
@@ -818,7 +870,7 @@ TempoMap::do_insert (MetricSection* section)
 
                                if (meter) {
                                        bool const ipm = insert_meter->position_lock_style() == MusicTime;
-                                       if ((ipm && meter->pulse() > insert_meter->pulse()) || (!ipm && meter->frame() > insert_meter->frame())) {
+                                       if ((ipm && meter->beat() > insert_meter->beat()) || (!ipm && meter->frame() > insert_meter->frame())) {
                                                break;
                                        }
                                }
@@ -837,44 +889,40 @@ TempoMap::do_insert (MetricSection* section)
                }
 
                _metrics.insert (i, section);
-               //dump (_metrics, std::cerr);
+               //dump (_metrics, std::cout);
        }
 }
 
-void
-TempoMap::replace_tempo (const TempoSection& ts, const Tempo& tempo, const double& pulse, TempoSection::Type type)
+TempoSection*
+TempoMap::add_tempo (const Tempo& tempo, const double& pulse, const framepos_t& frame, ARDOUR::TempoSection::Type type, PositionLockStyle pls)
 {
+       TempoSection* ts = 0;
        {
                Glib::Threads::RWLock::WriterLock lm (lock);
-               TempoSection& first (first_tempo());
-               if (ts.pulse() != first.pulse()) {
-                       remove_tempo_locked (ts);
-                       add_tempo_locked (tempo, pulse, true, type);
-               } else {
-                       first.set_type (type);
-                       {
-                               /* cannot move the first tempo section */
-                               *static_cast<Tempo*>(&first) = tempo;
-                               recompute_map (_metrics);
-                       }
-               }
+               ts = add_tempo_locked (tempo, pulse, frame, type, pls, true);
        }
 
+
        PropertyChanged (PropertyChange ());
+
+       return ts;
 }
 
 void
-TempoMap::replace_tempo (const TempoSection& ts, const Tempo& tempo, const framepos_t& frame, TempoSection::Type type)
+TempoMap::replace_tempo (const TempoSection& ts, const Tempo& tempo, const double& pulse, const framepos_t& frame, TempoSection::Type type, PositionLockStyle pls)
 {
+       const bool locked_to_meter = ts.locked_to_meter();
+
        {
                Glib::Threads::RWLock::WriterLock lm (lock);
                TempoSection& first (first_tempo());
                if (ts.frame() != first.frame()) {
                        remove_tempo_locked (ts);
-                       add_tempo_locked (tempo, frame, true, type);
+                       add_tempo_locked (tempo, pulse, frame, type, pls, true, locked_to_meter);
                } else {
                        first.set_type (type);
                        first.set_pulse (0.0);
+                       first.set_frame (frame);
                        first.set_position_lock_style (AudioTime);
                        {
                                /* cannot move the first tempo section */
@@ -887,87 +935,60 @@ TempoMap::replace_tempo (const TempoSection& ts, const Tempo& tempo, const frame
        PropertyChanged (PropertyChange ());
 }
 
-void
-TempoMap::add_tempo (const Tempo& tempo, const double& pulse, ARDOUR::TempoSection::Type type)
-{
-       {
-               Glib::Threads::RWLock::WriterLock lm (lock);
-               add_tempo_locked (tempo, pulse, true, type);
-       }
-
-       PropertyChanged (PropertyChange ());
-}
-
-void
-TempoMap::add_tempo (const Tempo& tempo, const framepos_t& frame, ARDOUR::TempoSection::Type type)
-{
-       {
-               Glib::Threads::RWLock::WriterLock lm (lock);
-               add_tempo_locked (tempo, frame, true, type);
-       }
-
-
-       PropertyChanged (PropertyChange ());
-}
-
-void
-TempoMap::add_tempo_locked (const Tempo& tempo, double pulse, bool recompute, ARDOUR::TempoSection::Type type)
+TempoSection*
+TempoMap::add_tempo_locked (const Tempo& tempo, double pulse, framepos_t frame
+                           , TempoSection::Type type, PositionLockStyle pls, bool recompute, bool locked_to_meter)
 {
-       TempoSection* ts = new TempoSection (pulse, tempo.beats_per_minute(), tempo.note_type(), type);
+       TempoSection* t = new TempoSection (pulse, frame, tempo.beats_per_minute(), tempo.note_type(), type, pls);
+       t->set_locked_to_meter (locked_to_meter);
 
-       do_insert (ts);
+       do_insert (t);
 
        if (recompute) {
-               solve_map (_metrics, ts, Tempo (ts->beats_per_minute(), ts->note_type()), ts->pulse());
+               if (pls == AudioTime) {
+                       solve_map_frame (_metrics, t, t->frame());
+               } else {
+                       solve_map_pulse (_metrics, t, t->pulse());
+               }
+               recompute_meters (_metrics);
        }
-}
-
-void
-TempoMap::add_tempo_locked (const Tempo& tempo, framepos_t frame, bool recompute, ARDOUR::TempoSection::Type type)
-{
-       TempoSection* ts = new TempoSection (frame, tempo.beats_per_minute(), tempo.note_type(), type);
-
-       do_insert (ts);
 
-       if (recompute) {
-               solve_map (_metrics, ts, Tempo (ts->beats_per_minute(), ts->note_type()), ts->frame());
-       }
+       return t;
 }
 
-void
-TempoMap::replace_meter (const MeterSection& ms, const Meter& meter, const BBT_Time& where)
+MeterSection*
+TempoMap::add_meter (const Meter& meter, const double& beat, const Timecode::BBT_Time& where, const framepos_t& frame, PositionLockStyle pls)
 {
+       MeterSection* m = 0;
        {
                Glib::Threads::RWLock::WriterLock lm (lock);
-               MeterSection& first (first_meter());
+               m = add_meter_locked (meter, beat, where, frame, pls, true);
+       }
 
-               const PositionLockStyle pl = ms.position_lock_style();
-               if (ms.pulse() != first.pulse()) {
-                       remove_meter_locked (ms);
-                       add_meter_locked (meter, pulse_at_beat_locked (_metrics, bbt_to_beats_locked (_metrics, where)), where, true);
-               } else {
-                       /* cannot move the first meter section */
-                       *static_cast<Meter*>(&first) = meter;
-                       first.set_position_lock_style (pl);
-                       recompute_map (_metrics);
-               }
+
+#ifndef NDEBUG
+       if (DEBUG_ENABLED(DEBUG::TempoMap)) {
+               dump (_metrics, std::cerr);
        }
+#endif
 
        PropertyChanged (PropertyChange ());
+       return m;
 }
 
 void
-TempoMap::replace_meter (const MeterSection& ms, const Meter& meter, const framepos_t& frame)
+TempoMap::replace_meter (const MeterSection& ms, const Meter& meter, const BBT_Time& where, const framepos_t& frame, PositionLockStyle pls)
 {
        {
                Glib::Threads::RWLock::WriterLock lm (lock);
-               MeterSection& first (first_meter());
-               TempoSection& first_t (first_tempo());
+               const double beat = beat_at_bbt_locked (_metrics, where);
 
-               if (ms.pulse() != first.pulse()) {
+               if (ms.movable()) {
                        remove_meter_locked (ms);
-                       add_meter_locked (meter, frame, true);
+                       add_meter_locked (meter, beat, where, frame, pls, true);
                } else {
+                       MeterSection& first (first_meter());
+                       TempoSection& first_t (first_tempo());
                        /* cannot move the first meter section */
                        *static_cast<Meter*>(&first) = meter;
                        first.set_position_lock_style (AudioTime);
@@ -975,389 +996,126 @@ TempoMap::replace_meter (const MeterSection& ms, const Meter& meter, const frame
                        first.set_frame (frame);
                        pair<double, BBT_Time> beat = make_pair (0.0, BBT_Time (1, 1, 0));
                        first.set_beat (beat);
-                       recompute_meters (_metrics);
                        first_t.set_frame (first.frame());
                        first_t.set_pulse (0.0);
                        first_t.set_position_lock_style (AudioTime);
-
                        recompute_map (_metrics);
                }
        }
+
        PropertyChanged (PropertyChange ());
 }
 
-
-void
-TempoMap::add_meter (const Meter& meter, const double& beat, const BBT_Time& where)
+MeterSection*
+TempoMap::add_meter_locked (const Meter& meter, double beat, const Timecode::BBT_Time& where, framepos_t frame, PositionLockStyle pls, bool recompute)
 {
-       {
-               Glib::Threads::RWLock::WriterLock lm (lock);
-               add_meter_locked (meter, beat, where, true);
+       const MeterSection& prev_m = meter_section_at_locked  (_metrics, frame - 1);
+       const double pulse = ((where.bars - prev_m.bbt().bars) * (prev_m.divisions_per_bar() / prev_m.note_divisor())) + prev_m.pulse();
+
+       if (pls == AudioTime) {
+               /* add meter-locked tempo */
+               add_tempo_locked (tempo_at_frame_locked (_metrics, frame), pulse,  frame, TempoSection::Ramp, AudioTime, true, true);
        }
 
+       MeterSection* new_meter = new MeterSection (pulse, frame, beat, where, meter.divisions_per_bar(), meter.note_divisor(), pls);
 
-#ifndef NDEBUG
-       if (DEBUG_ENABLED(DEBUG::TempoMap)) {
-               dump (_metrics, std::cerr);
+       do_insert (new_meter);
+
+       if (recompute) {
+
+               if (pls == AudioTime) {
+                       solve_map_frame (_metrics, new_meter, frame);
+               } else {
+                       solve_map_bbt (_metrics, new_meter, where);
+               }
        }
-#endif
 
-       PropertyChanged (PropertyChange ());
+       return new_meter;
 }
 
 void
-TempoMap::add_meter (const Meter& meter, const framepos_t& frame)
+TempoMap::change_initial_tempo (double beats_per_minute, double note_type)
 {
-       {
-               Glib::Threads::RWLock::WriterLock lm (lock);
-               add_meter_locked (meter, frame, true);
-       }
-
+       Tempo newtempo (beats_per_minute, note_type);
+       TempoSection* t;
 
-#ifndef NDEBUG
-       if (DEBUG_ENABLED(DEBUG::TempoMap)) {
-               dump (_metrics, std::cerr);
+       for (Metrics::iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
+               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                       if (!t->active()) {
+                               continue;
+                       }
+                       {
+                               Glib::Threads::RWLock::WriterLock lm (lock);
+                               *((Tempo*) t) = newtempo;
+                               recompute_map (_metrics);
+                       }
+                       PropertyChanged (PropertyChange ());
+                       break;
+               }
        }
-#endif
-
-       PropertyChanged (PropertyChange ());
 }
 
 void
-TempoMap::add_meter_locked (const Meter& meter, double beat, BBT_Time where, bool recompute)
+TempoMap::change_existing_tempo_at (framepos_t where, double beats_per_minute, double note_type)
 {
-       /* a new meter always starts a new bar on the first beat. so
-          round the start time appropriately. remember that
-          `where' is based on the existing tempo map, not
-          the result after we insert the new meter.
+       Tempo newtempo (beats_per_minute, note_type);
 
-       */
+       TempoSection* prev;
+       TempoSection* first;
+       Metrics::iterator i;
 
-       if (where.beats != 1) {
-               where.beats = 1;
-               where.bars++;
-       }
-       /* new meters *always* start on a beat. */
-       where.ticks = 0;
-       double pulse = pulse_at_beat_locked (_metrics, beat);
+       /* find the TempoSection immediately preceding "where"
+        */
 
-       MeterSection* new_meter = new MeterSection (pulse, beat, where, meter.divisions_per_bar(), meter.note_divisor());
-       do_insert (new_meter);
+       for (first = 0, i = _metrics.begin(), prev = 0; i != _metrics.end(); ++i) {
 
-       if (recompute) {
-               solve_map (_metrics, new_meter, Meter (meter.divisions_per_bar(), meter.note_divisor()), pulse);
-       }
+               if ((*i)->frame() > where) {
+                       break;
+               }
 
-}
+               TempoSection* t;
 
-void
-TempoMap::add_meter_locked (const Meter& meter, framepos_t frame, bool recompute)
-{
+               if ((t = dynamic_cast<TempoSection*>(*i)) != 0) {
+                       if (!t->active()) {
+                               continue;
+                       }
+                       if (!first) {
+                               first = t;
+                       }
+                       prev = t;
+               }
+       }
+
+       if (!prev) {
+               if (!first) {
+                       error << string_compose (_("no tempo sections defined in tempo map - cannot change tempo @ %1"), where) << endmsg;
+                       return;
+               }
 
-       MeterSection* new_meter = new MeterSection (frame, 0.0, meter.divisions_per_bar(), meter.note_divisor());
+               prev = first;
+       }
 
-       do_insert (new_meter);
+       /* reset */
 
-       if (recompute) {
-               solve_map (_metrics, new_meter, Meter (new_meter->divisions_per_bar(), new_meter->note_divisor()), frame);
+       {
+               Glib::Threads::RWLock::WriterLock lm (lock);
+               /* cannot move the first tempo section */
+               *((Tempo*)prev) = newtempo;
+               recompute_map (_metrics);
        }
 
+       PropertyChanged (PropertyChange ());
 }
 
-/**
-* This is for a gui that needs to know the frame of a tempo section if it were to be moved to some bbt time,
-* taking any possible reordering as a consequence of this into account.
-* @param section - the section to be altered
-* @param bpm - the new Tempo
-* @param bbt - the bbt where the altered tempo will fall
-* @return returns - the position in frames where the new tempo section will lie.
-*/
-framepos_t
-TempoMap::predict_tempo_frame (TempoSection* section, const Tempo& bpm, const BBT_Time& bbt)
+const MeterSection&
+TempoMap::first_meter () const
 {
-       Glib::Threads::RWLock::ReaderLock lm (lock);
-       Metrics future_map;
-       framepos_t ret = 0;
-       TempoSection* new_section = copy_metrics_and_point (future_map, section);
+       const MeterSection *m = 0;
 
-       double const beat = bbt_to_beats_locked (future_map, bbt);
-       if (solve_map (future_map, new_section, bpm, pulse_at_beat_locked (future_map, beat))) {
-               ret = new_section->frame();
-       } else {
-               ret = frame_at_beat_locked (_metrics, beat);
-       }
-
-       Metrics::const_iterator d = future_map.begin();
-       while (d != future_map.end()) {
-               delete (*d);
-               ++d;
-       }
-       return ret;
-}
-
-double
-TempoMap::predict_tempo_pulse (TempoSection* section, const Tempo& bpm, const framepos_t& frame)
-{
-       Glib::Threads::RWLock::ReaderLock lm (lock);
-       Metrics future_map;
-       double ret = 0.0;
-       TempoSection* new_section = copy_metrics_and_point (future_map, section);
-
-       if (solve_map (future_map, new_section, bpm, frame)) {
-               ret = new_section->pulse();
-       } else {
-               ret = pulse_at_frame_locked (_metrics, frame);
-       }
-
-       Metrics::const_iterator d = future_map.begin();
-       while (d != future_map.end()) {
-               delete (*d);
-               ++d;
-       }
-       return ret;
-}
-
-void
-TempoMap::gui_move_tempo_frame (TempoSection* ts,  const Tempo& bpm, const framepos_t& frame)
-{
-       Metrics future_map;
-       {
-               Glib::Threads::RWLock::WriterLock lm (lock);
-               TempoSection* new_section = copy_metrics_and_point (future_map, ts);
-               if (solve_map (future_map, new_section, bpm, frame)) {
-                       solve_map (_metrics, ts, bpm, frame);
-               }
-       }
-
-       Metrics::const_iterator d = future_map.begin();
-       while (d != future_map.end()) {
-               delete (*d);
-               ++d;
-       }
-
-       MetricPositionChanged (); // Emit Signal
-}
-
-void
-TempoMap::gui_move_tempo_beat (TempoSection* ts,  const Tempo& bpm, const double& beat)
-{
-       Metrics future_map;
-       {
-               Glib::Threads::RWLock::WriterLock lm (lock);
-               TempoSection* new_section = copy_metrics_and_point (future_map, ts);
-               if (solve_map (future_map, new_section, bpm, pulse_at_beat_locked (future_map, beat))) {
-                       solve_map (_metrics, ts, bpm,  pulse_at_beat_locked (_metrics, beat));
-               }
-       }
-
-       Metrics::const_iterator d = future_map.begin();
-       while (d != future_map.end()) {
-               delete (*d);
-               ++d;
-       }
-
-       MetricPositionChanged (); // Emit Signal
-}
-
-void
-TempoMap::gui_move_meter (MeterSection* ms, const Meter& mt, const framepos_t&  frame)
-{
-       {
-               Glib::Threads::RWLock::WriterLock lm (lock);
-               solve_map (_metrics, ms, mt, frame);
-       }
-
-       MetricPositionChanged (); // Emit Signal
-}
-
-void
-TempoMap::gui_move_meter (MeterSection* ms, const Meter& mt, const double&  beat)
-{
-       {
-               Glib::Threads::RWLock::WriterLock lm (lock);
-               solve_map (_metrics, ms, mt, pulse_at_beat_locked (_metrics, beat));
-       }
-
-       MetricPositionChanged (); // Emit Signal
-}
-
-bool
-TempoMap::gui_change_tempo (TempoSection* ts,  const Tempo& bpm)
-{
-       Metrics future_map;
-       bool can_solve = false;
-       {
-               Glib::Threads::RWLock::WriterLock lm (lock);
-               TempoSection* new_section = copy_metrics_and_point (future_map, ts);
-               new_section->set_beats_per_minute (bpm.beats_per_minute());
-               recompute_tempos (future_map);
-
-               if (check_solved (future_map, true)) {
-                       ts->set_beats_per_minute (bpm.beats_per_minute());
-                       recompute_map (_metrics);
-                       can_solve = true;
-               }
-       }
-
-       Metrics::const_iterator d = future_map.begin();
-       while (d != future_map.end()) {
-               delete (*d);
-               ++d;
-       }
-       if (can_solve) {
-               MetricPositionChanged (); // Emit Signal
-       }
-       return can_solve;
-}
-
-TempoSection*
-TempoMap::copy_metrics_and_point (Metrics& copy, TempoSection* section)
-{
-       TempoSection* t;
-       TempoSection* ret = 0;
-       MeterSection* m;
-
-       for (Metrics::iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
-                       if (t == section) {
-                               if (t->position_lock_style() == MusicTime) {
-                                       ret = new TempoSection (t->pulse(), t->beats_per_minute(), t->note_type(), t->type());
-                               } else {
-                                       ret = new TempoSection (t->frame(), t->beats_per_minute(), t->note_type(), t->type());
-                               }
-                               ret->set_active (t->active());
-                               ret->set_movable (t->movable());
-                               copy.push_back (ret);
-                               continue;
-                       }
-                       TempoSection* cp = 0;
-                       if (t->position_lock_style() == MusicTime) {
-                               cp = new TempoSection (t->pulse(), t->beats_per_minute(), t->note_type(), t->type());
-                       } else {
-                               cp = new TempoSection (t->frame(), t->beats_per_minute(), t->note_type(), t->type());
-                       }
-                       cp->set_active (t->active());
-                       cp->set_movable (t->movable());
-                       copy.push_back (cp);
-               }
-               if ((m = dynamic_cast<MeterSection *> (*i)) != 0) {
-                       if (m->position_lock_style() == MusicTime) {
-                               copy.push_back (new MeterSection (m->pulse(), m->beat(), m->bbt(), m->divisions_per_bar(), m->note_divisor()));
-                       } else {
-                               copy.push_back (new MeterSection (m->frame(), m->beat(), m->divisions_per_bar(), m->note_divisor()));
-                       }
-               }
-       }
-       recompute_map (copy);
-       return ret;
-}
-
-bool
-TempoMap::can_solve_bbt (TempoSection* ts,  const Tempo& bpm, const BBT_Time& bbt)
-{
-       Metrics copy;
-       TempoSection* new_section = 0;
-
-       {
-               Glib::Threads::RWLock::ReaderLock lm (lock);
-               new_section = copy_metrics_and_point (copy, ts);
-       }
-
-       double const beat = bbt_to_beats_locked (copy, bbt);
-       bool ret = solve_map (copy, new_section, bpm, pulse_at_beat_locked (copy, beat));
-
-       Metrics::const_iterator d = copy.begin();
-       while (d != copy.end()) {
-               delete (*d);
-               ++d;
-       }
-
-       return ret;
-}
-
-void
-TempoMap::change_initial_tempo (double beats_per_minute, double note_type)
-{
-       Tempo newtempo (beats_per_minute, note_type);
-       TempoSection* t;
-
-       for (Metrics::iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
-                       if (!t->active()) {
-                               continue;
-                       }
-                       {
-                               Glib::Threads::RWLock::WriterLock lm (lock);
-                               *((Tempo*) t) = newtempo;
-                               recompute_map (_metrics);
-                       }
-                       PropertyChanged (PropertyChange ());
-                       break;
-               }
-       }
-}
-
-void
-TempoMap::change_existing_tempo_at (framepos_t where, double beats_per_minute, double note_type)
-{
-       Tempo newtempo (beats_per_minute, note_type);
-
-       TempoSection* prev;
-       TempoSection* first;
-       Metrics::iterator i;
-
-       /* find the TempoSection immediately preceding "where"
-        */
-
-       for (first = 0, i = _metrics.begin(), prev = 0; i != _metrics.end(); ++i) {
-
-               if ((*i)->frame() > where) {
-                       break;
-               }
-
-               TempoSection* t;
-
-               if ((t = dynamic_cast<TempoSection*>(*i)) != 0) {
-                       if (!t->active()) {
-                               continue;
-                       }
-                       if (!first) {
-                               first = t;
-                       }
-                       prev = t;
-               }
-       }
-
-       if (!prev) {
-               if (!first) {
-                       error << string_compose (_("no tempo sections defined in tempo map - cannot change tempo @ %1"), where) << endmsg;
-                       return;
-               }
-
-               prev = first;
-       }
-
-       /* reset */
-
-       {
-               Glib::Threads::RWLock::WriterLock lm (lock);
-               /* cannot move the first tempo section */
-               *((Tempo*)prev) = newtempo;
-               recompute_map (_metrics);
-       }
-
-       PropertyChanged (PropertyChange ());
-}
-
-const MeterSection&
-TempoMap::first_meter () const
-{
-       const MeterSection *m = 0;
-
-       for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
-               if ((m = dynamic_cast<const MeterSection *> (*i)) != 0) {
-                       return *m;
-               }
+       for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
+               if ((m = dynamic_cast<const MeterSection *> (*i)) != 0) {
+                       return *m;
+               }
        }
 
        fatal << _("programming error: no meter section in tempo map!") << endmsg;
@@ -1395,7 +1153,9 @@ TempoMap::first_tempo () const
                        if (!t->active()) {
                                continue;
                        }
-                       return *t;
+                       if (!t->movable()) {
+                               return *t;
+                       }
                }
        }
 
@@ -1414,7 +1174,9 @@ TempoMap::first_tempo ()
                        if (!t->active()) {
                                continue;
                        }
-                       return *t;
+                       if (!t->movable()) {
+                               return *t;
+                       }
                }
        }
 
@@ -1425,7 +1187,7 @@ TempoMap::first_tempo ()
 void
 TempoMap::recompute_tempos (Metrics& metrics)
 {
-       TempoSection* prev_ts = 0;
+       TempoSection* prev_t = 0;
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
@@ -1434,62 +1196,103 @@ TempoMap::recompute_tempos (Metrics& metrics)
                        if (!t->active()) {
                                continue;
                        }
-                       if (prev_ts) {
+                       if (!t->movable()) {
+                               if (!prev_t) {
+                                       t->set_pulse (0.0);
+                                       prev_t = t;
+                                       continue;
+                               }
+                       }
+                       if (prev_t) {
                                if (t->position_lock_style() == AudioTime) {
-                                       prev_ts->set_c_func (prev_ts->compute_c_func_frame (t->pulses_per_minute(), t->frame(), _frame_rate));
-                                       t->set_pulse (prev_ts->pulse_at_tempo (t->pulses_per_minute(), t->frame(), _frame_rate));
+                                       prev_t->set_c_func (prev_t->compute_c_func_frame (t->pulses_per_minute(), t->frame(), _frame_rate));
+                                       if (!t->locked_to_meter()) {
+                                               t->set_pulse (prev_t->pulse_at_tempo (t->pulses_per_minute(), t->frame(), _frame_rate));
+                                       }
 
                                } else {
-                                       prev_ts->set_c_func (prev_ts->compute_c_func_pulse (t->pulses_per_minute(), t->pulse(), _frame_rate));
-                                       t->set_frame (prev_ts->frame_at_tempo (t->pulses_per_minute(), t->pulse(), _frame_rate));
+                                       prev_t->set_c_func (prev_t->compute_c_func_pulse (t->pulses_per_minute(), t->pulse(), _frame_rate));
+                                       t->set_frame (prev_t->frame_at_tempo (t->pulses_per_minute(), t->pulse(), _frame_rate));
 
                                }
                        }
-                       prev_ts = t;
+                       prev_t = t;
                }
        }
-       prev_ts->set_c_func (0.0);
+       prev_t->set_c_func (0.0);
 }
 
-/* tempos must be positioned correctly */
+/* tempos must be positioned correctly.
+   the current approach is to use a meter's bbt time as its base position unit.
+   an audio-locked meter requires a recomputation of pulse and beat (but not bbt),
+   while a music-locked meter requires recomputations of frame pulse and beat (but not bbt)
+*/
 void
 TempoMap::recompute_meters (Metrics& metrics)
 {
        MeterSection* meter = 0;
        MeterSection* prev_m = 0;
-       double accumulated_beats = 0.0;
-       uint32_t accumulated_bars = 0;
 
        for (Metrics::const_iterator mi = metrics.begin(); mi != metrics.end(); ++mi) {
                if ((meter = dynamic_cast<MeterSection*> (*mi)) != 0) {
-                       if (prev_m) {
-                               const double beats_in_m = (meter->pulse() - prev_m->pulse()) * prev_m->note_divisor();
-                               accumulated_beats += beats_in_m;
-                               accumulated_bars += (beats_in_m + 1) / prev_m->divisions_per_bar();
-                       }
                        if (meter->position_lock_style() == AudioTime) {
                                double pulse = 0.0;
-                               pair<double, BBT_Time> bt = make_pair (accumulated_beats, BBT_Time (accumulated_bars + 1, 1, 0));
-                               meter->set_beat (bt);
+                               pair<double, BBT_Time> b_bbt;
+                               TempoSection* meter_locked_tempo = 0;
+                               for (Metrics::const_iterator ii = metrics.begin(); ii != metrics.end(); ++ii) {
+                                       TempoSection* t;
+                                       if ((t = dynamic_cast<TempoSection*> (*ii)) != 0) {
+                                               if ((t->locked_to_meter() || !t->movable()) && t->frame() == meter->frame()) {
+                                                       meter_locked_tempo = t;
+                                                       break;
+                                               }
+                                       }
+                               }
+
                                if (prev_m) {
-                                       pulse = prev_m->pulse() + (meter->beat() - prev_m->beat()) / prev_m->note_divisor();
-                               } else {
-                                       if (meter->movable()) {
-                                               pulse = pulse_at_frame_locked (metrics, meter->frame());
-                                       } else {
-                                               pulse = 0.0;
+                                       const double beats = (meter->bbt().bars - prev_m->bbt().bars) * prev_m->divisions_per_bar();
+                                       if (beats + prev_m->beat() != meter->beat()) {
+                                               /* reordering caused a bbt change */
+                                               b_bbt = make_pair (beats + prev_m->beat()
+                                                                  , BBT_Time ((beats / prev_m->divisions_per_bar()) + prev_m->bbt().bars, 1, 0));
+                                               pulse = prev_m->pulse() + (beats / prev_m->note_divisor());
+
+                                       } else if (meter->movable()) {
+                                               b_bbt = make_pair (meter->beat(), meter->bbt());
+                                               pulse = prev_m->pulse() + (beats / prev_m->note_divisor());
                                        }
+                               } else {
+                                       b_bbt = make_pair (0.0, BBT_Time (1, 1, 0));
                                }
+                               if (meter_locked_tempo) {
+                                       meter_locked_tempo->set_pulse (pulse);
+                               }
+                               meter->set_beat (b_bbt);
                                meter->set_pulse (pulse);
+
                        } else {
+                               /* MusicTime */
                                double pulse = 0.0;
+                               pair<double, BBT_Time> b_bbt;
                                if (prev_m) {
-                                       pulse = prev_m->pulse() + (meter->beat() - prev_m->beat()) / prev_m->note_divisor();
+                                       const double beats = (meter->bbt().bars - prev_m->bbt().bars) * prev_m->divisions_per_bar();
+                                       if (beats + prev_m->beat() != meter->beat()) {
+                                               /* reordering caused a bbt change */
+                                               b_bbt = make_pair (beats + prev_m->beat()
+                                                                  , BBT_Time ((beats / prev_m->divisions_per_bar()) + prev_m->bbt().bars, 1, 0));
+                                       } else {
+                                               b_bbt = make_pair (beats + prev_m->beat(), meter->bbt());
+                                       }
+                                       pulse = (beats / prev_m->note_divisor()) + prev_m->pulse();
                                } else {
+                                       /* shouldn't happen - the first is audio-locked */
                                        pulse = pulse_at_beat_locked (metrics, meter->beat());
+                                       b_bbt = make_pair (meter->beat(), meter->bbt());
                                }
-                               meter->set_frame (frame_at_pulse_locked (metrics, pulse));
+
+                               meter->set_beat (b_bbt);
                                meter->set_pulse (pulse);
+                               meter->set_frame (frame_at_pulse_locked (metrics, pulse));
                        }
 
                        prev_m = meter;
@@ -1523,63 +1326,6 @@ TempoMap::recompute_map (Metrics& metrics, framepos_t end)
        recompute_meters (metrics);
 }
 
-double
-TempoMap::pulse_at_beat (const double& beat) const
-{
-       Glib::Threads::RWLock::ReaderLock lm (lock);
-       return pulse_at_beat_locked (_metrics, beat);
-}
-
-double
-TempoMap::pulse_at_beat_locked (const Metrics& metrics, const double& beat) const
-{
-       MeterSection* prev_ms = 0;
-       double accumulated_beats = 0.0;
-
-       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-                       if (prev_ms && m->beat() > beat) {
-                               break;
-                       }
-                       accumulated_beats = m->beat();
-                       prev_ms = m;
-               }
-
-       }
-       double const ret = prev_ms->pulse() + ((beat - accumulated_beats) / prev_ms->note_divisor());
-       return ret;
-}
-
-double
-TempoMap::beat_at_pulse (const double& pulse) const
-{
-       Glib::Threads::RWLock::ReaderLock lm (lock);
-       return beat_at_pulse_locked (_metrics, pulse);
-}
-
-double
-TempoMap::beat_at_pulse_locked (const Metrics& metrics, const double& pulse) const
-{
-       MeterSection* prev_ms = 0;
-       double accumulated_beats = 0.0;
-
-       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-                       if (prev_ms && m->pulse() > pulse) {
-                               break;
-                       }
-                       accumulated_beats = m->beat();
-                       prev_ms = m;
-               }
-       }
-
-       double const beats_in_section = (pulse - prev_ms->pulse()) * prev_ms->note_divisor();
-
-       return beats_in_section + accumulated_beats;
-}
-
 TempoMetric
 TempoMap::metric_at (framepos_t frame, Metrics::const_iterator* last) const
 {
@@ -1639,211 +1385,137 @@ TempoMap::metric_at (BBT_Time bbt) const
        return m;
 }
 
-void
-TempoMap::bbt_time (framepos_t frame, BBT_Time& bbt)
-{
-
-       if (frame < 0) {
-               bbt.bars = 1;
-               bbt.beats = 1;
-               bbt.ticks = 0;
-               warning << string_compose (_("tempo map asked for BBT time at frame %1\n"), frame) << endmsg;
-               return;
-       }
-       Glib::Threads::RWLock::ReaderLock lm (lock);
-       double const beat = beat_at_frame_locked (_metrics, frame);
-
-       bbt = beats_to_bbt_locked (_metrics, beat);
-}
-
 double
-TempoMap::bbt_to_beats (const Timecode::BBT_Time& bbt)
+TempoMap::beat_at_frame (const framecnt_t& frame) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-
-       return bbt_to_beats_locked (_metrics, bbt);
+       return beat_at_frame_locked (_metrics, frame);
 }
 
+/* meter / tempo section based */
 double
-TempoMap::bbt_to_beats_locked (const Metrics& metrics, const Timecode::BBT_Time& bbt) const
+TempoMap::beat_at_frame_locked (const Metrics& metrics, const framecnt_t& frame) const
 {
-       /* CALLER HOLDS READ LOCK */
+       const TempoSection& ts = tempo_section_at_locked (metrics, frame);
+       MeterSection* prev_m = 0;
+       MeterSection* next_m = 0;
 
-       double accumulated_beats = 0.0;
-       double accumulated_bars = 0.0;
-       MeterSection* prev_ms = 0;
-       /* because audio-locked meters have 'fake' integral beats,
-          there is no pulse offset here.
-       */
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                MeterSection* m;
                if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-                       double bars_to_m = 0.0;
-                       if (prev_ms) {
-                               bars_to_m = (m->beat() - prev_ms->beat()) / prev_ms->divisions_per_bar();
-                               if ((bars_to_m + accumulated_bars) > (bbt.bars - 1)) {
-                                       break;
-                               }
-                               accumulated_beats = m->beat();
-                               accumulated_bars += bars_to_m;
+                       if (prev_m && m->frame() > frame) {
+                               next_m = m;
+                               break;
                        }
-                       prev_ms = m;
+                       prev_m = m;
                }
        }
+       if (frame < prev_m->frame()) {
+               return 0.0;
+       }
+       const double beat = prev_m->beat() + (ts.pulse_at_frame (frame, _frame_rate) - prev_m->pulse()) * prev_m->note_divisor();
 
-       double const remaining_bars = (bbt.bars - 1) - accumulated_bars;
-       double const remaining_bars_in_beats = remaining_bars * prev_ms->divisions_per_bar();
-       double const ret = remaining_bars_in_beats + accumulated_beats + (bbt.beats - 1) + (bbt.ticks / BBT_Time::ticks_per_beat);
+       if (next_m && next_m->beat() < beat) {
+               return next_m->beat();
+       }
 
-       return ret;
+       return beat;
 }
 
-Timecode::BBT_Time
-TempoMap::beats_to_bbt (const double& beats)
+framecnt_t
+TempoMap::frame_at_beat (const double& beat) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-
-       return beats_to_bbt_locked (_metrics, beats);
+       return frame_at_beat_locked (_metrics, beat);
 }
 
-Timecode::BBT_Time
-TempoMap::beats_to_bbt_locked (const Metrics& metrics, const double& b) const
+/* meter section based */
+framecnt_t
+TempoMap::frame_at_beat_locked (const Metrics& metrics, const double& beat) const
 {
-       /* CALLER HOLDS READ LOCK */
-       MeterSection* prev_ms = 0;
-       const double beats = (b < 0.0) ? 0.0 : b;
-       uint32_t accumulated_bars = 0;
-       double accumulated_beats = 0.0;
+       const TempoSection& prev_t = tempo_section_at_beat_locked (metrics, beat);
+       MeterSection* prev_m = 0;
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m = 0;
-
+               MeterSection* m;
                if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-
-                       if (prev_ms) {
-                               double const beats_to_m = m->beat() - prev_ms->beat();
-                               if (accumulated_beats + beats_to_m > beats) {
-                                       /* this is the meter after the one our beat is on*/
-                                       break;
-                               }
-
-                               /* we need a whole number of bars. */
-                               accumulated_bars += (beats_to_m + 1) / prev_ms->divisions_per_bar();
-                               accumulated_beats += beats_to_m;
+                       if (prev_m && m->beat() > beat) {
+                               break;
                        }
-
-                       prev_ms = m;
+                       prev_m = m;
                }
        }
 
-       double const beats_in_ms = beats - accumulated_beats;
-       uint32_t const bars_in_ms = (uint32_t) floor (beats_in_ms / prev_ms->divisions_per_bar());
-       uint32_t const total_bars = bars_in_ms + accumulated_bars;
-       double const remaining_beats = beats_in_ms - (bars_in_ms * prev_ms->divisions_per_bar());
-       double const remaining_ticks = (remaining_beats - floor (remaining_beats)) * BBT_Time::ticks_per_beat;
-
-       BBT_Time ret;
+       return prev_t.frame_at_pulse (((beat - prev_m->beat()) / prev_m->note_divisor()) + prev_m->pulse(), _frame_rate);
+}
 
-       ret.ticks = (uint32_t) floor (remaining_ticks + 0.5);
-       ret.beats = (uint32_t) floor (remaining_beats);
-       ret.bars = total_bars;
+double
+TempoMap::pulse_at_beat (const double& beat) const
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       return pulse_at_beat_locked (_metrics, beat);
+}
 
-       /* 0 0 0 to 1 1 0 - based mapping*/
-       ++ret.bars;
-       ++ret.beats;
+double
+TempoMap::pulse_at_beat_locked (const Metrics& metrics, const double& beat) const
+{
+       MeterSection* prev_m = 0;
 
-       if (ret.ticks >= BBT_Time::ticks_per_beat) {
-               ++ret.beats;
-               ret.ticks -= BBT_Time::ticks_per_beat;
-       }
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               MeterSection* m;
+               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+                       if (prev_m && m->beat() > beat) {
+                               break;
+                       }
+                       prev_m = m;
+               }
 
-       if (ret.beats >= prev_ms->divisions_per_bar() + 1) {
-               ++ret.bars;
-               ret.beats = 1;
        }
-
+       double const ret = prev_m->pulse() + ((beat - prev_m->beat()) / prev_m->note_divisor());
        return ret;
 }
 
-Timecode::BBT_Time
-TempoMap::pulse_to_bbt (const double& pulse)
+double
+TempoMap::beat_at_pulse (const double& pulse) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-       MeterSection* prev_ms = 0;
-       uint32_t accumulated_bars = 0;
-       double accumulated_pulses = 0.0;
+       return beat_at_pulse_locked (_metrics, pulse);
+}
 
-       for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
-               MeterSection* m = 0;
+double
+TempoMap::beat_at_pulse_locked (const Metrics& metrics, const double& pulse) const
+{
+       MeterSection* prev_m = 0;
 
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               MeterSection* m;
                if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-
-                       if (prev_ms) {
-                               double const pulses_to_m = m->pulse() - prev_ms->pulse();
-                               if (accumulated_pulses + pulses_to_m > pulse) {
-                                       /* this is the meter after the one our beat is on*/
+                       if (prev_m && m->pulse() > pulse) {
+                               if (((pulse - prev_m->pulse()) * prev_m->note_divisor()) + prev_m->beat() > m->beat()) {
                                        break;
                                }
-
-                               /* we need a whole number of bars. */
-                               accumulated_pulses += pulses_to_m;
-                               accumulated_bars += ((pulses_to_m * prev_ms->note_divisor()) + 1) / prev_ms->divisions_per_bar();
                        }
-
-                       prev_ms = m;
+                       prev_m = m;
                }
        }
-       double const beats_in_ms = (pulse - prev_ms->pulse()) * prev_ms->note_divisor();
-       uint32_t const bars_in_ms = (uint32_t) floor (beats_in_ms / prev_ms->divisions_per_bar());
-       uint32_t const total_bars = bars_in_ms + accumulated_bars;
-       double const remaining_beats = beats_in_ms - (bars_in_ms * prev_ms->divisions_per_bar());
-       double const remaining_ticks = (remaining_beats - floor (remaining_beats)) * BBT_Time::ticks_per_beat;
-
-       BBT_Time ret;
-
-       ret.ticks = (uint32_t) floor (remaining_ticks + 0.5);
-       ret.beats = (uint32_t) floor (remaining_beats);
-       ret.bars = total_bars;
-
-       /* 0 0 0 to 1 1 0 mapping*/
-       ++ret.bars;
-       ++ret.beats;
-
-       if (ret.ticks >= BBT_Time::ticks_per_beat) {
-               ++ret.beats;
-               ret.ticks -= BBT_Time::ticks_per_beat;
-       }
-
-       if (ret.beats >= prev_ms->divisions_per_bar() + 1) {
-               ++ret.bars;
-               ret.beats = 1;
-       }
 
+       double const ret = ((pulse - prev_m->pulse()) * prev_m->note_divisor()) + prev_m->beat();
        return ret;
 }
 
 double
-TempoMap::beat_at_frame (const framecnt_t& frame) const
+TempoMap::pulse_at_frame (const framecnt_t& frame) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-       return beat_at_frame_locked (_metrics, frame);
-}
-
-double
-TempoMap::beat_at_frame_locked (const Metrics& metrics, const framecnt_t& frame) const
-{
-       framecnt_t const offset_frame = frame + frame_offset_at (metrics, frame);
-       double const pulse = pulse_at_frame_locked (metrics, offset_frame);
-
-       return beat_at_pulse_locked (metrics, pulse);
+       return pulse_at_frame_locked (_metrics, frame);
 }
 
+/* tempo section based */
 double
 TempoMap::pulse_at_frame_locked (const Metrics& metrics, const framecnt_t& frame) const
 {
        /* HOLD (at least) THE READER LOCK */
-       TempoSection* prev_ts = 0;
-       double accumulated_pulses = 0.0;
+       TempoSection* prev_t = 0;
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
@@ -1851,44 +1523,35 @@ TempoMap::pulse_at_frame_locked (const Metrics& metrics, const framecnt_t& frame
                        if (!t->active()) {
                                continue;
                        }
-                       if (prev_ts && t->frame() > frame) {
+                       if (prev_t && t->frame() > frame) {
                                /*the previous ts is the one containing the frame */
-                               double const ret = prev_ts->pulse_at_frame (frame, _frame_rate);
+                               const double ret = prev_t->pulse_at_frame (frame, _frame_rate);
                                return ret;
                        }
-                       accumulated_pulses = t->pulse();
-                       prev_ts = t;
+                       prev_t = t;
                }
        }
 
        /* treated as constant for this ts */
-       double const pulses_in_section = (frame - prev_ts->frame()) / prev_ts->frames_per_pulse (_frame_rate);
+       const double pulses_in_section = (frame - prev_t->frame()) / prev_t->frames_per_pulse (_frame_rate);
 
-       return pulses_in_section + accumulated_pulses;
+       return pulses_in_section + prev_t->pulse();
 }
 
 framecnt_t
-TempoMap::frame_at_beat (const double& beat) const
+TempoMap::frame_at_pulse (const double& pulse) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-       return frame_at_beat_locked (_metrics, beat);
-}
-
-framecnt_t
-TempoMap::frame_at_beat_locked (const Metrics& metrics, const double& beat) const
-{
-       framecnt_t const frame = frame_at_pulse_locked (metrics, pulse_at_beat_locked (metrics, beat));
-       frameoffset_t const frame_off = frame_offset_at (metrics, frame);
-       return frame - frame_off;
+       return frame_at_pulse_locked (_metrics, pulse);
 }
 
+/* tempo section based */
 framecnt_t
 TempoMap::frame_at_pulse_locked (const Metrics& metrics, const double& pulse) const
 {
        /* HOLD THE READER LOCK */
 
-       const TempoSection* prev_ts = 0;
-       double accumulated_pulses = 0.0;
+       const TempoSection* prev_t = 0;
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
@@ -1897,155 +1560,385 @@ TempoMap::frame_at_pulse_locked (const Metrics& metrics, const double& pulse) co
                        if (!t->active()) {
                                continue;
                        }
-                       if (prev_ts && t->pulse() > pulse) {
-                               return prev_ts->frame_at_pulse (pulse, _frame_rate);
+                       if (prev_t && t->pulse() > pulse) {
+                               return prev_t->frame_at_pulse (pulse, _frame_rate);
                        }
 
-                       accumulated_pulses = t->pulse();
-                       prev_ts = t;
+                       prev_t = t;
                }
        }
        /* must be treated as constant, irrespective of _type */
-       double const pulses_in_section = pulse - accumulated_pulses;
-       double const dtime = pulses_in_section * prev_ts->frames_per_pulse (_frame_rate);
+       double const pulses_in_section = pulse - prev_t->pulse();
+       double const dtime = pulses_in_section * prev_t->frames_per_pulse (_frame_rate);
 
-       framecnt_t const ret = (framecnt_t) floor (dtime) + prev_ts->frame();
+       framecnt_t const ret = (framecnt_t) floor (dtime) + prev_t->frame();
 
        return ret;
 }
 
+const Tempo
+TempoMap::tempo_at_frame (const framepos_t& frame) const
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       return tempo_at_frame_locked (_metrics, frame);
+}
+
+const Tempo
+TempoMap::tempo_at_frame_locked (const Metrics& metrics, const framepos_t& frame) const
+{
+       TempoSection* prev_t = 0;
+
+       Metrics::const_iterator i;
+
+       for (i = _metrics.begin(); i != _metrics.end(); ++i) {
+               TempoSection* t;
+               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                       if (!t->active()) {
+                               continue;
+                       }
+                       if ((prev_t) && t->frame() > frame) {
+                               /* t is the section past frame */
+                               const double ret_bpm = prev_t->tempo_at_frame (frame, _frame_rate) * prev_t->note_type();
+                               const Tempo ret_tempo (ret_bpm, prev_t->note_type());
+                               return ret_tempo;
+                       }
+                       prev_t = t;
+               }
+       }
+
+       const double ret = prev_t->beats_per_minute();
+       const Tempo ret_tempo (ret, prev_t->note_type ());
+
+       return ret_tempo;
+}
+
+
+double
+TempoMap::beat_at_bbt (const Timecode::BBT_Time& bbt)
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       return beat_at_bbt_locked (_metrics, bbt);
+}
+
+
 double
-TempoMap::beat_offset_at (const Metrics& metrics, const double& beat) const
+TempoMap::beat_at_bbt_locked (const Metrics& metrics, const Timecode::BBT_Time& bbt) const
 {
+       /* CALLER HOLDS READ LOCK */
+
        MeterSection* prev_m = 0;
-       double beat_off = first_meter().pulse();
 
+       /* because audio-locked meters have 'fake' integral beats,
+          there is no pulse offset here.
+       */
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m = 0;
+               MeterSection* m;
                if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
                        if (prev_m) {
-                               if (m->beat() > beat) {
+                               const double bars_to_m = (m->beat() - prev_m->beat()) / prev_m->divisions_per_bar();
+                               if ((bars_to_m + (prev_m->bbt().bars - 1)) > (bbt.bars - 1)) {
                                        break;
                                }
-
-                               if (m->position_lock_style() == AudioTime) {
-                                       beat_off += ((m->beat() - prev_m->beat()) / prev_m->note_divisor()) - floor (m->pulse() - prev_m->pulse());
-                               }
                        }
                        prev_m = m;
                }
        }
 
-       return beat_off;
+       const double remaining_bars = bbt.bars - prev_m->bbt().bars;
+       const double remaining_bars_in_beats = remaining_bars * prev_m->divisions_per_bar();
+       const double ret = remaining_bars_in_beats + prev_m->beat() + (bbt.beats - 1) + (bbt.ticks / BBT_Time::ticks_per_beat);
+
+       return ret;
+}
+
+Timecode::BBT_Time
+TempoMap::bbt_at_beat (const double& beats)
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       return bbt_at_beat_locked (_metrics, beats);
 }
 
-frameoffset_t
-TempoMap::frame_offset_at (const Metrics& metrics, const framepos_t& frame) const
+Timecode::BBT_Time
+TempoMap::bbt_at_beat_locked (const Metrics& metrics, const double& b) const
 {
-       frameoffset_t frame_off = 0;
+       /* CALLER HOLDS READ LOCK */
        MeterSection* prev_m = 0;
+       const double beats = max (0.0, b);
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                MeterSection* m = 0;
+
                if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-                       if (m->frame() > frame) {
-                               break;
-                       }
-                       if (prev_m && m->position_lock_style() == AudioTime) {
-                               const double pulse = prev_m->pulse() + ((m->beat() - prev_m->beat()) / prev_m->note_divisor());
-                               frame_off += frame_at_pulse_locked (metrics, pulse) - m->frame();
+                       if (prev_m) {
+                               if (m->beat() > beats) {
+                                       /* this is the meter after the one our beat is on*/
+                                       break;
+                               }
                        }
+
                        prev_m = m;
                }
        }
 
-       return frame_off;
-}
+       const double beats_in_ms = beats - prev_m->beat();
+       const uint32_t bars_in_ms = (uint32_t) floor (beats_in_ms / prev_m->divisions_per_bar());
+       const uint32_t total_bars = bars_in_ms + (prev_m->bbt().bars - 1);
+       const double remaining_beats = beats_in_ms - (bars_in_ms * prev_m->divisions_per_bar());
+       const double remaining_ticks = (remaining_beats - floor (remaining_beats)) * BBT_Time::ticks_per_beat;
 
-framepos_t
-TempoMap::frame_time (const BBT_Time& bbt)
-{
-       if (bbt.bars < 1) {
-               warning << string_compose (_("tempo map asked for frame time at bar < 1  (%1)\n"), bbt) << endmsg;
-               return 0;
-       }
+       BBT_Time ret;
 
-       if (bbt.beats < 1) {
-               throw std::logic_error ("beats are counted from one");
-       }
-       Glib::Threads::RWLock::ReaderLock lm (lock);
-       double const beat = bbt_to_beats_locked (_metrics, bbt);
-       framecnt_t const frame = frame_at_beat_locked (_metrics, beat);
-       return frame;
-}
+       ret.ticks = (uint32_t) floor (remaining_ticks + 0.5);
+       ret.beats = (uint32_t) floor (remaining_beats);
+       ret.bars = total_bars;
 
-framepos_t
+       /* 0 0 0 to 1 1 0 - based mapping*/
+       ++ret.bars;
+       ++ret.beats;
+
+       if (ret.ticks >= BBT_Time::ticks_per_beat) {
+               ++ret.beats;
+               ret.ticks -= BBT_Time::ticks_per_beat;
+       }
+
+       if (ret.beats >= prev_m->divisions_per_bar() + 1) {
+               ++ret.bars;
+               ret.beats = 1;
+       }
+
+       return ret;
+}
+
+double
+TempoMap::pulse_at_bbt (const Timecode::BBT_Time& bbt)
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+
+       return pulse_at_bbt_locked (_metrics, bbt);
+}
+
+double
+TempoMap::pulse_at_bbt_locked (const Metrics& metrics, const Timecode::BBT_Time& bbt) const
+{
+       /* CALLER HOLDS READ LOCK */
+
+       MeterSection* prev_m = 0;
+
+       /* because audio-locked meters have 'fake' integral beats,
+          there is no pulse offset here.
+       */
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               MeterSection* m;
+               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+                       if (prev_m) {
+                               if (m->bbt().bars > bbt.bars) {
+                                       break;
+                               }
+                       }
+                       prev_m = m;
+               }
+       }
+
+       const double remaining_bars = bbt.bars - prev_m->bbt().bars;
+       const double remaining_pulses = remaining_bars * prev_m->divisions_per_bar() / prev_m->note_divisor();
+       const double ret = remaining_pulses + prev_m->pulse() + (((bbt.beats - 1) + (bbt.ticks / BBT_Time::ticks_per_beat)) / prev_m->note_divisor());
+
+       return ret;
+}
+
+Timecode::BBT_Time
+TempoMap::bbt_at_pulse (const double& pulse)
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+
+       return bbt_at_pulse_locked (_metrics, pulse);
+}
+
+Timecode::BBT_Time
+TempoMap::bbt_at_pulse_locked (const Metrics& metrics, const double& pulse) const
+{
+       MeterSection* prev_m = 0;
+
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               MeterSection* m = 0;
+
+               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+
+                       if (prev_m) {
+                               double const pulses_to_m = m->pulse() - prev_m->pulse();
+                               if (prev_m->pulse() + pulses_to_m > pulse) {
+                                       /* this is the meter after the one our beat is on*/
+                                       break;
+                               }
+                       }
+
+                       prev_m = m;
+               }
+       }
+
+       const double beats_in_ms = (pulse - prev_m->pulse()) * prev_m->note_divisor();
+       const uint32_t bars_in_ms = (uint32_t) floor (beats_in_ms / prev_m->divisions_per_bar());
+       const uint32_t total_bars = bars_in_ms + (prev_m->bbt().bars - 1);
+       const double remaining_beats = beats_in_ms - (bars_in_ms * prev_m->divisions_per_bar());
+       const double remaining_ticks = (remaining_beats - floor (remaining_beats)) * BBT_Time::ticks_per_beat;
+
+       BBT_Time ret;
+
+       ret.ticks = (uint32_t) floor (remaining_ticks + 0.5);
+       ret.beats = (uint32_t) floor (remaining_beats);
+       ret.bars = total_bars;
+
+       /* 0 0 0 to 1 1 0 mapping*/
+       ++ret.bars;
+       ++ret.beats;
+
+       if (ret.ticks >= BBT_Time::ticks_per_beat) {
+               ++ret.beats;
+               ret.ticks -= BBT_Time::ticks_per_beat;
+       }
+
+       if (ret.beats >= prev_m->divisions_per_bar() + 1) {
+               ++ret.bars;
+               ret.beats = 1;
+       }
+
+       return ret;
+}
+
+void
+TempoMap::bbt_time (framepos_t frame, BBT_Time& bbt)
+{
+
+       if (frame < 0) {
+               bbt.bars = 1;
+               bbt.beats = 1;
+               bbt.ticks = 0;
+               warning << string_compose (_("tempo map asked for BBT time at frame %1\n"), frame) << endmsg;
+               return;
+       }
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       const double beat = beat_at_frame_locked (_metrics, frame);
+
+       bbt = bbt_at_beat_locked (_metrics, beat);
+}
+
+framepos_t
+TempoMap::frame_time (const BBT_Time& bbt)
+{
+       if (bbt.bars < 1) {
+               warning << string_compose (_("tempo map asked for frame time at bar < 1  (%1)\n"), bbt) << endmsg;
+               return 0;
+       }
+
+       if (bbt.beats < 1) {
+               throw std::logic_error ("beats are counted from one");
+       }
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+
+       return frame_time_locked (_metrics, bbt);
+}
+
+/* meter section based */
+framepos_t
 TempoMap::frame_time_locked (const Metrics& metrics, const BBT_Time& bbt) const
 {
        /* HOLD THE READER LOCK */
 
-       framepos_t const ret = frame_at_pulse_locked (metrics, pulse_at_beat_locked (metrics, bbt_to_beats_locked (metrics, bbt)));
-
+       const framepos_t ret = frame_at_beat_locked (metrics, beat_at_bbt_locked (metrics, bbt));
        return ret;
 }
 
 bool
-TempoMap::check_solved (Metrics& metrics, bool by_frame)
+TempoMap::check_solved (const Metrics& metrics) const
 {
-       TempoSection* prev_ts = 0;
+       TempoSection* prev_t = 0;
+       MeterSection* prev_m = 0;
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
+               MeterSection* m;
                if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
                        if (!t->active()) {
                                continue;
                        }
-                       if (prev_ts) {
-                               if ((by_frame && t->frame() < prev_ts->frame()) || (!by_frame && t->pulse() < prev_ts->pulse())) {
+                       if (prev_t) {
+                               if ((t->frame() <= prev_t->frame()) || (t->pulse() <= prev_t->pulse())) {
                                        return false;
                                }
-                               if (by_frame && t->frame() != prev_ts->frame_at_pulse (t->pulse(), _frame_rate)) {
-                                       return false;
+
+                               /* precision check ensures tempo and frames align.*/
+                               if (t->frame() != prev_t->frame_at_tempo (t->pulses_per_minute(), t->pulse(), _frame_rate)) {
+                                       if (!t->locked_to_meter()) {
+                                               return false;
+                                       }
                                }
-                               /*
-                               if (!by_frame && fabs (t->pulse() - prev_ts->pulse_at_tempo (t->pulses_per_minute(), t->frame(), _frame_rate)) > 0.00001) {
-                                       std::cerr << "beat precision too low for bpm: " << t->beats_per_minute() << std::endl <<
-                                               " |error          :" << t->pulse() - prev_ts->pulse_at_tempo (t->pulses_per_minute(), t->frame(), _frame_rate) << std::endl <<
-                                               "|frame at beat   :" << prev_ts->frame_at_pulse (t->pulse(), _frame_rate) << std::endl <<
-                                               " |frame at tempo : " << prev_ts->frame_at_tempo (t->pulses_per_minute(), t->pulse(), _frame_rate) << std::endl;
+                       }
+                       prev_t = t;
+               }
+
+               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+                       if (prev_m && m->position_lock_style() == AudioTime) {
+                               TempoSection* t = const_cast<TempoSection*>(&tempo_section_at_locked (metrics, m->frame() - 1));
+                               const double nascent_m_pulse = ((m->beat() - prev_m->beat()) / prev_m->note_divisor()) + prev_m->pulse();
+                               const framepos_t nascent_m_frame = t->frame_at_pulse (nascent_m_pulse, _frame_rate);
+
+                               if (t && (nascent_m_frame > m->frame() || nascent_m_frame < 0)) {
                                        return false;
                                }
-                               */
                        }
-                       prev_ts = t;
+
+                       prev_m = m;
                }
+
        }
 
        return true;
 }
 
 bool
-TempoMap::solve_map (Metrics& imaginary, TempoSection* section, const Tempo& bpm, const framepos_t& frame)
+TempoMap::set_active_tempos (const Metrics& metrics, const framepos_t& frame)
 {
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               TempoSection* t;
+               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                       if (!t->movable()) {
+                               t->set_active (true);
+                               continue;
+                       }
+                       if (t->movable() && t->active () && t->position_lock_style() == AudioTime && t->frame() < frame) {
+                               t->set_active (false);
+                               t->set_pulse (0.0);
+                       } else if (t->movable() && t->position_lock_style() == AudioTime && t->frame() > frame) {
+                               t->set_active (true);
+                       } else if (t->movable() && t->position_lock_style() == AudioTime && t->frame() == frame) {
+                               return false;
+                       }
+               }
+       }
+       return true;
+}
 
-       TempoSection* prev_ts = 0;
+bool
+TempoMap::solve_map_frame (Metrics& imaginary, TempoSection* section, const framepos_t& frame)
+{
+       TempoSection* prev_t = 0;
        TempoSection* section_prev = 0;
-       MetricSectionFrameSorter fcmp;
-       MetricSectionSorter cmp;
        framepos_t first_m_frame = 0;
+
        for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
                MeterSection* m;
                if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
                        if (!m->movable()) {
                                first_m_frame = m->frame();
+                               break;
                        }
                }
        }
        if (section->movable() && frame <= first_m_frame) {
                return false;
-       } else {
-               section->set_active (true);
        }
+
+       section->set_active (true);
        section->set_frame (frame);
 
        for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
@@ -2055,80 +1948,54 @@ TempoMap::solve_map (Metrics& imaginary, TempoSection* section, const Tempo& bpm
                        if (!t->active()) {
                                continue;
                        }
-                       if (prev_ts) {
+                       if (prev_t) {
                                if (t == section) {
-                                       section_prev = prev_ts;
+                                       section_prev = prev_t;
                                        continue;
                                }
                                if (t->position_lock_style() == MusicTime) {
-                                       prev_ts->set_c_func (prev_ts->compute_c_func_pulse (t->pulses_per_minute(), t->pulse(), _frame_rate));
-                                       t->set_frame (prev_ts->frame_at_pulse (t->pulse(), _frame_rate));
+                                       prev_t->set_c_func (prev_t->compute_c_func_pulse (t->pulses_per_minute(), t->pulse(), _frame_rate));
+                                       t->set_frame (prev_t->frame_at_pulse (t->pulse(), _frame_rate));
                                } else {
-                                       prev_ts->set_c_func (prev_ts->compute_c_func_frame (t->pulses_per_minute(), t->frame(), _frame_rate));
-                                       t->set_pulse (prev_ts->pulse_at_frame (t->frame(), _frame_rate));
+                                       prev_t->set_c_func (prev_t->compute_c_func_frame (t->pulses_per_minute(), t->frame(), _frame_rate));
+                                       if (!t->locked_to_meter()) {
+                                               t->set_pulse (prev_t->pulse_at_frame (t->frame(), _frame_rate));
+                                       }
                                }
                        }
-                       prev_ts = t;
+                       prev_t = t;
                }
        }
 
        if (section_prev) {
                section_prev->set_c_func (section_prev->compute_c_func_frame (section->pulses_per_minute(), frame, _frame_rate));
-               section->set_pulse (section_prev->pulse_at_frame (frame, _frame_rate));
+               if (!section->locked_to_meter()) {
+                       section->set_pulse (section_prev->pulse_at_frame (frame, _frame_rate));
+               }
        }
 
-       if (section->position_lock_style() == MusicTime) {
-               /* we're setting the frame */
-               section->set_position_lock_style (AudioTime);
-               recompute_tempos (imaginary);
-               section->set_position_lock_style (MusicTime);
-       } else {
-               recompute_tempos (imaginary);
-       }
+       recompute_tempos (imaginary);
 
-       if (check_solved (imaginary, true)) {
-               recompute_meters (imaginary);
+       if (check_solved (imaginary)) {
                return true;
        }
 
+       MetricSectionFrameSorter fcmp;
        imaginary.sort (fcmp);
-       if (section->position_lock_style() == MusicTime) {
-               /* we're setting the frame */
-               section->set_position_lock_style (AudioTime);
-               recompute_tempos (imaginary);
-               section->set_position_lock_style (MusicTime);
-       } else {
-               recompute_tempos (imaginary);
-       }
-       if (check_solved (imaginary, true)) {
-               recompute_meters (imaginary);
-               return true;
-       }
 
-       imaginary.sort (cmp);
-       if (section->position_lock_style() == MusicTime) {
-               /* we're setting the frame */
-               section->set_position_lock_style (AudioTime);
-               recompute_tempos (imaginary);
-               section->set_position_lock_style (MusicTime);
-       } else {
-               recompute_tempos (imaginary);
-       }
-       if (check_solved (imaginary, true)) {
-               recompute_meters (imaginary);
+       recompute_tempos (imaginary);
+
+       if (check_solved (imaginary)) {
                return true;
        }
-       //dump (imaginary, std::cerr);
 
        return false;
 }
 
 bool
-TempoMap::solve_map (Metrics& imaginary, TempoSection* section, const Tempo& bpm, const double& pulse)
+TempoMap::solve_map_pulse (Metrics& imaginary, TempoSection* section, const double& pulse)
 {
-       MetricSectionSorter cmp;
-       MetricSectionFrameSorter fcmp;
-       TempoSection* prev_ts = 0;
+       TempoSection* prev_t = 0;
        TempoSection* section_prev = 0;
 
        section->set_pulse (pulse);
@@ -2139,222 +2006,659 @@ TempoMap::solve_map (Metrics& imaginary, TempoSection* section, const Tempo& bpm
                        if (!t->active()) {
                                continue;
                        }
-                       if (prev_ts) {
+                       if (!t->movable()) {
+                               t->set_pulse (0.0);
+                               prev_t = t;
+                               continue;
+                       }
+                       if (prev_t) {
                                if (t == section) {
-                                       section_prev = prev_ts;
+                                       section_prev = prev_t;
                                        continue;
                                }
                                if (t->position_lock_style() == MusicTime) {
-                                       prev_ts->set_c_func (prev_ts->compute_c_func_pulse (t->pulses_per_minute(), t->pulse(), _frame_rate));
-                                       t->set_frame (prev_ts->frame_at_pulse (t->pulse(), _frame_rate));
+                                       prev_t->set_c_func (prev_t->compute_c_func_pulse (t->pulses_per_minute(), t->pulse(), _frame_rate));
+                                       t->set_frame (prev_t->frame_at_pulse (t->pulse(), _frame_rate));
                                } else {
-                                       prev_ts->set_c_func (prev_ts->compute_c_func_frame (t->pulses_per_minute(), t->frame(), _frame_rate));
-                                       t->set_pulse (prev_ts->pulse_at_frame (t->frame(), _frame_rate));
+                                       prev_t->set_c_func (prev_t->compute_c_func_frame (t->pulses_per_minute(), t->frame(), _frame_rate));
+                                       if (!t->locked_to_meter()) {
+                                               t->set_pulse (prev_t->pulse_at_frame (t->frame(), _frame_rate));
+                                       }
                                }
                        }
-                       prev_ts = t;
+                       prev_t = t;
                }
        }
+
        if (section_prev) {
                section_prev->set_c_func (section_prev->compute_c_func_pulse (section->pulses_per_minute(), pulse, _frame_rate));
                section->set_frame (section_prev->frame_at_pulse (pulse, _frame_rate));
        }
 
-       if (section->position_lock_style() == AudioTime) {
-               /* we're setting the pulse */
-               section->set_position_lock_style (MusicTime);
-               recompute_tempos (imaginary);
-               section->set_position_lock_style (AudioTime);
-       } else {
-               recompute_tempos (imaginary);
-       }
-       if (check_solved (imaginary, false)) {
-               recompute_meters (imaginary);
-               return true;
-       }
+       recompute_tempos (imaginary);
+
+       if (check_solved (imaginary)) {
+               return true;
+       }
+
+       MetricSectionSorter cmp;
+       imaginary.sort (cmp);
+
+       recompute_tempos (imaginary);
+       /* Reordering
+        * XX need a restriction here, but only for this case,
+        * as audio locked tempos don't interact in the same way.
+        *
+        * With music-locked tempos, the solution to cross-dragging can fly off the screen
+        * e.g.
+        * |50 bpm                        |250 bpm |60 bpm
+        *                drag 250 to the pulse after 60->
+        * a clue: dragging the second 60 <- past the 250 would cause no such problem.
+        */
+       if (check_solved (imaginary)) {
+               return true;
+       }
+
+       return false;
+}
+
+bool
+TempoMap::solve_map_frame (Metrics& imaginary, MeterSection* section, const framepos_t& frame)
+{
+       /* disallow moving first meter past any subsequent one, and any movable meter before the first one */
+       const MeterSection* other =  &meter_section_at_locked (imaginary, frame);
+       if ((!section->movable() && other->movable()) || (!other->movable() && section->movable() && other->frame() >= frame)) {
+               return false;
+       }
+
+       if (!section->movable()) {
+               /* lock the first tempo to our first meter */
+               if (!set_active_tempos (imaginary, frame)) {
+                       return false;
+               }
+       }
+
+       /* it would make sense to bail out if there is no audio-locked meter,
+          however it may be desirable to move a music-locked meter by frame at some point.
+       */
+       TempoSection* meter_locked_tempo = 0;
+       for (Metrics::const_iterator ii = imaginary.begin(); ii != imaginary.end(); ++ii) {
+               TempoSection* t;
+               if ((t = dynamic_cast<TempoSection*> (*ii)) != 0) {
+                       if ((t->locked_to_meter() || !t->movable()) && t->frame() == section->frame()) {
+                               meter_locked_tempo = t;
+                               break;
+                       }
+               }
+       }
+
+       if (!meter_locked_tempo) {
+               return false;
+       }
+
+       MeterSection* prev_m = 0;
+       Metrics future_map;
+       TempoSection* tempo_copy = copy_metrics_and_point (imaginary, future_map, meter_locked_tempo);
+       bool solved = false;
+
+       for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
+               MeterSection* m;
+               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+                       if (m == section){
+                               if (prev_m && section->movable()) {
+                                       const double beats = (pulse_at_frame_locked (imaginary, frame) - prev_m->pulse()) * prev_m->note_divisor();
+                                       if (beats + prev_m->beat() < section->beat()) {
+                                               /* set the frame/pulse corresponding to its musical position,
+                                                * as an earlier time than this has been requested.
+                                               */
+                                               const double new_pulse = ((section->beat() - prev_m->beat())
+                                                                         / prev_m->note_divisor()) + prev_m->pulse();
+
+                                               const framepos_t smallest_frame = frame_at_pulse_locked (future_map, new_pulse);
+
+                                               if ((solved = solve_map_frame (future_map, tempo_copy, smallest_frame))) {
+                                                       meter_locked_tempo->set_pulse (new_pulse);
+                                                       solve_map_frame (imaginary, meter_locked_tempo, smallest_frame);
+                                                       section->set_frame (smallest_frame);
+                                                       section->set_pulse (new_pulse);
+                                               } else {
+                                                       solved = false;
+                                               }
+
+                                               Metrics::const_iterator d = future_map.begin();
+                                               while (d != future_map.end()) {
+                                                       delete (*d);
+                                                       ++d;
+                                               }
+
+                                               if (!solved) {
+                                                       return false;
+                                               }
+                                       } else {
+                                               /* all is ok. set section's tempo */
+                                               MeterSection* meter_copy = const_cast<MeterSection*> (&meter_section_at_locked (future_map, section->frame()));
+                                               meter_copy->set_frame (frame);
+
+                                               if ((solved = solve_map_frame (future_map, tempo_copy, frame))) {
+                                                       section->set_frame (frame);
+                                                       meter_locked_tempo->set_pulse (((section->beat() - prev_m->beat())
+                                                                                               / prev_m->note_divisor()) + prev_m->pulse());
+                                                       solve_map_frame (imaginary, meter_locked_tempo, frame);
+                                               } else {
+                                                       solved = false;
+                                               }
+
+                                               Metrics::const_iterator d = future_map.begin();
+                                               while (d != future_map.end()) {
+                                                       delete (*d);
+                                                       ++d;
+                                               }
+
+                                               if (!solved) {
+                                                       return false;
+                                               }
+                                       }
+                               } else {
+                                       /* not movable (first meter atm) */
+
+                                       tempo_copy->set_frame (frame);
+                                       tempo_copy->set_pulse (0.0);
+
+                                       if ((solved = solve_map_frame (future_map, tempo_copy, frame))) {
+                                               section->set_frame (frame);
+                                               meter_locked_tempo->set_frame (frame);
+                                               meter_locked_tempo->set_pulse (0.0);
+                                               solve_map_frame (imaginary, meter_locked_tempo, frame);
+                                       } else {
+                                               solved = false;
+                                       }
+
+                                       Metrics::const_iterator d = future_map.begin();
+                                       while (d != future_map.end()) {
+                                               delete (*d);
+                                               ++d;
+                                       }
+
+                                       if (!solved) {
+                                               return false;
+                                       }
+
+                                       pair<double, BBT_Time> b_bbt = make_pair (0.0, BBT_Time (1, 1, 0));
+                                       section->set_beat (b_bbt);
+                                       section->set_pulse (0.0);
+
+                               }
+                               break;
+                       }
+
+                       prev_m = m;
+               }
+       }
+
+       MetricSectionFrameSorter fcmp;
+       imaginary.sort (fcmp);
+
+       recompute_meters (imaginary);
+
+       return true;
+}
+
+bool
+TempoMap::solve_map_bbt (Metrics& imaginary, MeterSection* section, const BBT_Time& when)
+{
+       /* disallow setting section to an existing meter's bbt */
+       for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
+               MeterSection* m;
+               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+                       if (m != section && m->bbt().bars == when.bars) {
+                               return false;
+                       }
+               }
+       }
+
+       MeterSection* prev_m = 0;
+       MeterSection* section_prev = 0;
+
+       for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
+               MeterSection* m;
+               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+                       pair<double, BBT_Time> b_bbt;
+                       double new_pulse = 0.0;
+
+                       if (prev_m && m->bbt().bars > when.bars && !section_prev){
+                               section_prev = prev_m;
+                               const double beats = (when.bars - section_prev->bbt().bars) * section_prev->divisions_per_bar();
+                               const double pulse = (beats / section_prev->note_divisor()) + section_prev->pulse();
+                               pair<double, BBT_Time> b_bbt = make_pair (beats + section_prev->beat(), when);
+
+                               section->set_beat (b_bbt);
+                               section->set_pulse (pulse);
+                               section->set_frame (frame_at_pulse_locked (imaginary, pulse));
+                               prev_m = section;
+                               continue;
+                       }
+
+                       if (m->position_lock_style() == AudioTime) {
+                               TempoSection* meter_locked_tempo = 0;
+
+                               for (Metrics::const_iterator ii = imaginary.begin(); ii != imaginary.end(); ++ii) {
+                                       TempoSection* t;
+                                       if ((t = dynamic_cast<TempoSection*> (*ii)) != 0) {
+                                               if ((t->locked_to_meter() || !t->movable()) && t->frame() == m->frame()) {
+                                                       meter_locked_tempo = t;
+                                                       break;
+                                               }
+                                       }
+                               }
+
+                               if (!meter_locked_tempo) {
+                                       return false;
+                               }
+
+                               if (prev_m) {
+                                       const double beats = ((m->bbt().bars - prev_m->bbt().bars) * prev_m->divisions_per_bar());
+
+                                       if (beats + prev_m->beat() != m->beat()) {
+                                               /* tempo/ meter change caused a change in beat (bar). */
+                                               b_bbt = make_pair (beats + prev_m->beat()
+                                                                  , BBT_Time ((beats / prev_m->divisions_per_bar()) + prev_m->bbt().bars, 1, 0));
+                                               new_pulse = prev_m->pulse() + (beats / prev_m->note_divisor());
+                                       } else if (m->movable()) {
+                                               b_bbt = make_pair (m->beat(), m->bbt());
+                                               new_pulse = prev_m->pulse() + (beats / prev_m->note_divisor());
+                                       }
+                               } else {
+                                       b_bbt = make_pair (0.0, BBT_Time (1, 1, 0));
+                               }
+
+                               meter_locked_tempo->set_pulse (new_pulse);
+                               m->set_beat (b_bbt);
+                               m->set_pulse (new_pulse);
+
+                       } else {
+                               /* MusicTime */
+                               const double beats = ((m->bbt().bars - prev_m->bbt().bars) * prev_m->divisions_per_bar());
+                               if (beats + prev_m->beat() != m->beat()) {
+                                       /* tempo/ meter change caused a change in beat (bar). */
+                                       b_bbt = make_pair (beats + prev_m->beat()
+                                                          , BBT_Time ((beats / prev_m->divisions_per_bar()) + prev_m->bbt().bars, 1, 0));
+                               } else {
+                                       b_bbt = make_pair (beats + prev_m->beat()
+                                                          , m->bbt());
+                               }
+                               new_pulse = (beats / prev_m->note_divisor()) + prev_m->pulse();
+                               m->set_beat (b_bbt);
+                               m->set_pulse (new_pulse);
+                               m->set_frame (frame_at_pulse_locked (imaginary, new_pulse));
+                       }
+
+                       prev_m = m;
+               }
+       }
+
+       if (!section_prev) {
+
+               const double beats = (when.bars - prev_m->bbt().bars) * prev_m->divisions_per_bar();
+               const double pulse = (beats / prev_m->note_divisor()) + prev_m->pulse();
+               pair<double, BBT_Time> b_bbt = make_pair (beats + prev_m->beat(), when);
+
+               section->set_beat (b_bbt);
+               section->set_pulse (pulse);
+               section->set_frame (frame_at_pulse_locked (imaginary, pulse));
+       }
+
+       MetricSectionSorter cmp;
+       imaginary.sort (cmp);
+
+       recompute_meters (imaginary);
+
+       return true;
+}
+
+/** places a copy of _metrics into copy and returns a pointer
+ *  to section's equivalent in copy.
+ */
+TempoSection*
+TempoMap::copy_metrics_and_point (const Metrics& metrics, Metrics& copy, TempoSection* section)
+{
+       TempoSection* ret = 0;
+
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               TempoSection* t;
+               MeterSection* m;
+               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                       if (t == section) {
+                               ret = new TempoSection (*t);
+                               copy.push_back (ret);
+                               continue;
+                       }
+
+                       TempoSection* cp = new TempoSection (*t);
+                       copy.push_back (cp);
+               }
+               if ((m = dynamic_cast<MeterSection *> (*i)) != 0) {
+                       MeterSection* cp = new MeterSection (*m);
+                       copy.push_back (cp);
+               }
+       }
+
+       return ret;
+}
+
+MeterSection*
+TempoMap::copy_metrics_and_point (const Metrics& metrics, Metrics& copy, MeterSection* section)
+{
+       MeterSection* ret = 0;
+
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               TempoSection* t;
+               MeterSection* m;
+               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                       TempoSection* cp = new TempoSection (*t);
+                       copy.push_back (cp);
+               }
+
+               if ((m = dynamic_cast<MeterSection *> (*i)) != 0) {
+                       if (m == section) {
+                               ret = new MeterSection (*m);
+                               copy.push_back (ret);
+                               continue;
+                       }
+                       MeterSection* cp = new MeterSection (*m);
+                       copy.push_back (cp);
+               }
+       }
+
+       return ret;
+}
+
+bool
+TempoMap::can_solve_bbt (TempoSection* ts, const BBT_Time& bbt)
+{
+       Metrics copy;
+       TempoSection* tempo_copy = 0;
+
+       {
+               Glib::Threads::RWLock::ReaderLock lm (lock);
+               tempo_copy = copy_metrics_and_point (_metrics, copy, ts);
+               if (!tempo_copy) {
+                       return false;
+               }
+       }
+
+       const bool ret = solve_map_pulse (copy, tempo_copy, pulse_at_bbt_locked (copy, bbt));
+
+       Metrics::const_iterator d = copy.begin();
+       while (d != copy.end()) {
+               delete (*d);
+               ++d;
+       }
+
+       return ret;
+}
+
+/**
+* This is for a gui that needs to know the pulse or frame of a tempo section if it were to be moved to some bbt time,
+* taking any possible reordering as a consequence of this into account.
+* @param section - the section to be altered
+* @param bbt - the bbt where the altered tempo will fall
+* @return returns - the position in pulses and frames (as a pair) where the new tempo section will lie.
+*/
+pair<double, framepos_t>
+TempoMap::predict_tempo_position (TempoSection* section, const BBT_Time& bbt)
+{
+       Metrics future_map;
+       pair<double, framepos_t> ret = make_pair (0.0, 0);
+
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+
+       TempoSection* tempo_copy = copy_metrics_and_point (_metrics, future_map, section);
+
+       const double beat = beat_at_bbt_locked (future_map, bbt);
+
+       if (solve_map_pulse (future_map, tempo_copy, pulse_at_beat_locked (future_map, beat))) {
+               ret.first = tempo_copy->pulse();
+               ret.second = tempo_copy->frame();
+       } else {
+               ret.first = section->pulse();
+               ret.second = section->frame();
+       }
+
+       Metrics::const_iterator d = future_map.begin();
+       while (d != future_map.end()) {
+               delete (*d);
+               ++d;
+       }
+       return ret;
+}
+
+void
+TempoMap::gui_move_tempo (TempoSection* ts, const framepos_t& frame)
+{
+       Metrics future_map;
+
+       if (ts->position_lock_style() == MusicTime) {
+               {
+                       Glib::Threads::RWLock::WriterLock lm (lock);
+                       TempoSection* tempo_copy = copy_metrics_and_point (_metrics, future_map, ts);
+                       const double pulse = pulse_at_frame_locked (future_map, frame);
+                       if (solve_map_pulse (future_map, tempo_copy, pulse)) {
+                               solve_map_pulse (_metrics, ts, pulse);
+                               recompute_meters (_metrics);
+                       }
+               }
+
+       } else {
+
+               {
+                       Glib::Threads::RWLock::WriterLock lm (lock);
+                       TempoSection* tempo_copy = copy_metrics_and_point (_metrics, future_map, ts);
+                       if (solve_map_frame (future_map, tempo_copy, frame)) {
+                               solve_map_frame (_metrics, ts, frame);
+                               recompute_meters (_metrics);
+                       }
+               }
+       }
+
+       Metrics::const_iterator d = future_map.begin();
+       while (d != future_map.end()) {
+               delete (*d);
+               ++d;
+       }
+
+       MetricPositionChanged (); // Emit Signal
+}
+
+void
+TempoMap::gui_move_meter (MeterSection* ms, const framepos_t& frame)
+{
+       Metrics future_map;
+
+       if (ms->position_lock_style() == AudioTime) {
 
-       imaginary.sort (cmp);
-       if (section->position_lock_style() == AudioTime) {
-               /* we're setting the pulse */
-               section->set_position_lock_style (MusicTime);
-               recompute_tempos (imaginary);
-               section->set_position_lock_style (AudioTime);
+               {
+                       Glib::Threads::RWLock::WriterLock lm (lock);
+                       MeterSection* copy = copy_metrics_and_point (_metrics, future_map, ms);
+
+                       if (solve_map_frame (future_map, copy, frame)) {
+                               solve_map_frame (_metrics, ms, frame);
+                               recompute_tempos (_metrics);
+                       }
+               }
        } else {
-               recompute_tempos (imaginary);
-       }
+               {
+                       Glib::Threads::RWLock::WriterLock lm (lock);
+                       MeterSection* copy = copy_metrics_and_point (_metrics, future_map, ms);
 
-       if (check_solved (imaginary, false)) {
-               recompute_meters (imaginary);
-               return true;
-       }
+                       const double beat = beat_at_frame_locked (_metrics, frame);
+                       const Timecode::BBT_Time bbt = bbt_at_beat_locked (_metrics, beat);
 
-       imaginary.sort (fcmp);
-       if (section->position_lock_style() == AudioTime) {
-               /* we're setting the pulse */
-               section->set_position_lock_style (MusicTime);
-               recompute_tempos (imaginary);
-               section->set_position_lock_style (AudioTime);
-       } else {
-               recompute_tempos (imaginary);
+                       if (solve_map_bbt (future_map, copy, bbt)) {
+                               solve_map_bbt (_metrics, ms, bbt);
+                               recompute_tempos (_metrics);
+                       }
+               }
        }
 
-       if (check_solved (imaginary, false)) {
-               recompute_meters (imaginary);
-               return true;
+       Metrics::const_iterator d = future_map.begin();
+       while (d != future_map.end()) {
+               delete (*d);
+               ++d;
        }
 
-       //dump (imaginary, std::cerr);
-
-       return false;
+       MetricPositionChanged (); // Emit Signal
 }
 
-void
-TempoMap::solve_map (Metrics& imaginary, MeterSection* section, const Meter& mt, const double& pulse)
+bool
+TempoMap::gui_change_tempo (TempoSection* ts, const Tempo& bpm)
 {
-       MeterSection* prev_ms = 0;
-       double accumulated_beats = 0.0;
-       uint32_t accumulated_bars = 0;
-
-       section->set_pulse (pulse);
+       Metrics future_map;
+       bool can_solve = false;
+       {
+               Glib::Threads::RWLock::WriterLock lm (lock);
+               TempoSection* tempo_copy = copy_metrics_and_point (_metrics, future_map, ts);
+               tempo_copy->set_beats_per_minute (bpm.beats_per_minute());
+               recompute_tempos (future_map);
 
-       for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
-               MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-                       if (prev_ms) {
-                               double const beats_in_m = (m->pulse() - prev_ms->pulse()) * prev_ms->note_divisor();
-                               accumulated_beats += beats_in_m;
-                               accumulated_bars += (beats_in_m + 1) / prev_ms->divisions_per_bar();
-                       }
-                       if (m == section){
-                               section->set_frame (frame_at_pulse_locked (imaginary, pulse));
-                               pair<double, BBT_Time> b_bbt = make_pair (accumulated_beats, BBT_Time (accumulated_bars + 1, 1, 0));
-                               section->set_beat (b_bbt);
-                               prev_ms = section;
-                               continue;
-                       }
-                       if (prev_ms) {
-                               if (m->position_lock_style() == MusicTime) {
-                                       const double pulse = prev_ms->pulse() + (m->beat() - prev_ms->beat()) / prev_ms->note_divisor();
-                                       m->set_frame (frame_at_pulse_locked (imaginary, pulse));
-                                       m->set_pulse (pulse);
-                               } else {
-                                       pair<double, BBT_Time> b_bbt = make_pair (accumulated_beats, BBT_Time (accumulated_bars + 1, 1, 0));
-                                       m->set_beat (b_bbt);
-                                       const double pulse = prev_ms->pulse() + (m->beat() - prev_ms->beat()) / prev_ms->note_divisor();
-                                       m->set_pulse (pulse);
-                               }
-                       }
-                       prev_ms = m;
+               if (check_solved (future_map)) {
+                       ts->set_beats_per_minute (bpm.beats_per_minute());
+                       recompute_map (_metrics);
+                       can_solve = true;
                }
        }
 
-       if (section->position_lock_style() == AudioTime) {
-               /* we're setting the pulse */
-               section->set_position_lock_style (MusicTime);
-               recompute_meters (imaginary);
-               section->set_position_lock_style (AudioTime);
-       } else {
-               recompute_meters (imaginary);
+       Metrics::const_iterator d = future_map.begin();
+       while (d != future_map.end()) {
+               delete (*d);
+               ++d;
+       }
+       if (can_solve) {
+               MetricPositionChanged (); // Emit Signal
        }
+       return can_solve;
 }
 
 void
-TempoMap::solve_map (Metrics& imaginary, MeterSection* section, const Meter& mt, const framepos_t& frame)
-{
-       MeterSection* prev_ms = 0;
+TempoMap::gui_dilate_tempo (TempoSection* ts, const framepos_t& frame, const framepos_t& end_frame, const double& pulse)
+{
+       /*
+         Ts (future prev_t)   Tnext
+         |                    |
+         |     [drag^]        |
+         |----------|----------
+               e_f  pulse(frame)
+       */
 
-       if (!section->movable()) {
-               TempoSection* first_t;
-               for (Metrics::const_iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
-                       TempoSection* t;
+       Metrics future_map;
+
+       {
+               Glib::Threads::RWLock::WriterLock lm (lock);
+
+               if (!ts) {
+                       return;
+               }
+
+               TempoSection* prev_t = copy_metrics_and_point (_metrics, future_map, ts);
+               TempoSection* prev_to_prev_t = 0;
+               const frameoffset_t fr_off = end_frame - frame;
+
+               if (prev_t && prev_t->pulse() > 0.0) {
+                       prev_to_prev_t = const_cast<TempoSection*>(&tempo_section_at_locked (future_map, prev_t->frame() - 1));
+               }
+
+               TempoSection* next_t = 0;
+               for (Metrics::iterator i = future_map.begin(); i != future_map.end(); ++i) {
+                       TempoSection* t = 0;
                        if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
-                               if (!t->movable()) {
-                                       t->set_active (true);
-                                       first_t = t;
-                               }
-                               if (t->movable() && t->active () && t->position_lock_style() == AudioTime && t->frame() < frame) {
-                                       t->set_active (false);
-                                       t->set_pulse (0.0);
-                               } else if (t->movable() && t->position_lock_style() == AudioTime && t->frame() > frame) {
-                                       t->set_active (true);
-                               } else if (t->movable() && t->position_lock_style() == AudioTime && t->frame() == frame) {
-                                       return;
+                               if (t->frame() > ts->frame()) {
+                                       next_t = t;
+                                       break;
                                }
                        }
                }
 
-               Metrics future_map;
-               TempoSection* new_section = copy_metrics_and_point (future_map, first_t);
-
-               new_section->set_frame (frame);
-               new_section->set_pulse (0.0);
-               new_section->set_active (true);
+               /* the change in frames is the result of changing the slope of at most 2 previous tempo sections.
+                  constant to constant is straightforward, as the tempo prev to prev_t has constant slope.
+               */
+               double contribution = 0.0;
+               double start_pulse = prev_t->pulse_at_frame (frame, _frame_rate);
 
-               if (solve_map (future_map, new_section, Tempo (new_section->beats_per_minute(), new_section->note_type()), frame)) {
-                       first_t->set_frame (frame);
-                       first_t->set_pulse (0.0);
-                       first_t->set_active (true);
-                       solve_map (imaginary, first_t, Tempo (first_t->beats_per_minute(), first_t->note_type()), frame);
-               } else {
-                       return;
+               if (next_t && prev_to_prev_t && prev_to_prev_t->type() == TempoSection::Ramp) {
+                       contribution = (prev_t->frame() - prev_to_prev_t->frame()) / (double) (next_t->frame() - prev_to_prev_t->frame());
                }
-       }
 
-       double accumulated_beats = 0.0;
-       uint32_t accumulated_bars = 0;
+               frameoffset_t prev_t_frame_contribution = fr_off - (contribution * (double) fr_off);
+               double end_pulse = prev_t->pulse_at_frame (end_frame, _frame_rate);
+               double new_bpm;
 
-       section->set_frame (frame);
+               if (prev_t->type() == TempoSection::Constant || prev_t->c_func() == 0.0) {
+
+                       if (prev_t->position_lock_style() == MusicTime) {
+                               if (prev_to_prev_t && prev_to_prev_t->type() == TempoSection::Ramp) {
+
+                                       new_bpm = prev_t->beats_per_minute() * ((frame - prev_to_prev_t->frame())
+                                                                               / (double) ((frame + prev_t_frame_contribution) - prev_to_prev_t->frame()));
 
-       for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
-               MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-                       if (prev_ms) {
-                               const double beats_in_m = (m->pulse() - prev_ms->pulse()) * prev_ms->note_divisor();
-                               accumulated_beats += beats_in_m;
-                               accumulated_bars += (beats_in_m + 1) / prev_ms->divisions_per_bar();
-                       }
-                       if (m == section){
-                               /*
-                                 here we define the pulse for this frame.
-                                 we're going to set it 'incorrectly' to the next integer and use this 'error'
-                                 as an offset to the map as far as users of the public methods are concerned.
-                                 (meters should go on absolute pulses to keep us sane)
-                               */
-                               pair<double, BBT_Time> b_bbt = make_pair (accumulated_beats, BBT_Time (accumulated_bars + 1, 1, 0));
-                               if (m->movable()) {
-                                       m->set_pulse (pulse_at_frame_locked (imaginary, frame));
                                } else {
-                                       m->set_pulse (0.0);
+                                       /* prev to prev is irrelevant */
+
+                                       if (start_pulse != prev_t->pulse()) {
+                                               new_bpm = prev_t->beats_per_minute() * ((start_pulse - prev_t->pulse()) / (end_pulse - prev_t->pulse()));
+                                       } else {
+                                               new_bpm = prev_t->beats_per_minute();
+                                       }
                                }
-                               m->set_beat (b_bbt);
-                               prev_ms = m;
-                               continue;
-                       }
-                       if (prev_ms) {
-                               if (m->position_lock_style() == MusicTime) {
-                                       const double pulse = prev_ms->pulse() + (m->beat() - prev_ms->beat()) / prev_ms->note_divisor();
-                                       m->set_frame (frame_at_pulse_locked (imaginary, pulse));
-                                       m->set_pulse (pulse);
+                       } else {
+                               /* AudioTime */
+                               if (prev_to_prev_t && prev_to_prev_t->type() == TempoSection::Ramp) {
+                                       new_bpm = prev_t->beats_per_minute() * ((frame - prev_t->frame())
+                                                                               / (double) ((frame + prev_t_frame_contribution) - prev_t->frame()));
                                } else {
-                                       pair<double, BBT_Time> b_bbt = make_pair (accumulated_beats, BBT_Time (accumulated_bars + 1, 1, 0));
-                                       m->set_beat (b_bbt);
-                                       const double pulse = prev_ms->pulse() + (m->beat() - prev_ms->beat()) / prev_ms->note_divisor();
-                                       m->set_pulse (pulse);
+                                       /* prev_to_prev_t is irrelevant */
+
+                                       if (end_frame != prev_t->frame()) {
+                                               new_bpm = prev_t->beats_per_minute() * ((frame - prev_t->frame()) / (double) (end_frame - prev_t->frame()));
+                                       } else {
+                                               new_bpm = prev_t->beats_per_minute();
+                                       }
                                }
                        }
-                       prev_ms = m;
+               } else {
+
+                       double frame_ratio;
+                       double pulse_ratio;
+                       const framepos_t pulse_pos = prev_t->frame_at_pulse (pulse, _frame_rate);
+
+                       if (prev_to_prev_t) {
+
+                               frame_ratio = (((pulse_pos - fr_off) - prev_to_prev_t->frame()) / (double) ((pulse_pos) - prev_to_prev_t->frame()));
+                               pulse_ratio = ((start_pulse - prev_to_prev_t->pulse()) / (end_pulse - prev_to_prev_t->pulse()));
+                       } else {
+
+                               frame_ratio = (((pulse_pos - fr_off) - prev_t->frame()) / (double) ((pulse_pos) - prev_t->frame()));
+                               pulse_ratio = (start_pulse / end_pulse);
+                       }
+                       new_bpm = prev_t->beats_per_minute() * (pulse_ratio * frame_ratio);
+               }
+
+               prev_t->set_beats_per_minute (new_bpm);
+               recompute_tempos (future_map);
+               recompute_meters (future_map);
+
+               if (check_solved (future_map)) {
+                       ts->set_beats_per_minute (new_bpm);
+                       recompute_tempos (_metrics);
+                       recompute_meters (_metrics);
                }
        }
 
-       if (section->position_lock_style() == MusicTime) {
-               /* we're setting the frame */
-               section->set_position_lock_style (AudioTime);
-               recompute_meters (imaginary);
-               section->set_position_lock_style (MusicTime);
-       } else {
-               recompute_meters (imaginary);
+       Metrics::const_iterator d = future_map.begin();
+       while (d != future_map.end()) {
+               delete (*d);
+               ++d;
        }
-       //dump (imaginary, std::cerr);
+
+       MetricPositionChanged (); // Emit Signal
 }
 
 framecnt_t
@@ -2362,13 +2666,11 @@ TempoMap::bbt_duration_at (framepos_t pos, const BBT_Time& bbt, int dir)
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
 
-       double const tick_at_time = beat_at_frame_locked (_metrics, pos) * BBT_Time::ticks_per_beat;
-       double const bbt_ticks = bbt.ticks + (bbt.beats * BBT_Time::ticks_per_beat);
-       double const total_beats = (tick_at_time + bbt_ticks) / BBT_Time::ticks_per_beat;
-       framecnt_t const time_at_bbt = frame_at_beat_locked (_metrics, total_beats);
-       framecnt_t const ret = time_at_bbt;
+       const double tick_at_time = beat_at_frame_locked (_metrics, pos) * BBT_Time::ticks_per_beat;
+       const double bbt_ticks = bbt.ticks + (bbt.beats * BBT_Time::ticks_per_beat);
+       const double total_beats = (tick_at_time + bbt_ticks) / BBT_Time::ticks_per_beat;
 
-       return ret;
+       return frame_at_beat_locked (_metrics, total_beats);
 }
 
 framepos_t
@@ -2474,69 +2776,18 @@ TempoMap::round_to_beat_subdivision (framepos_t fr, int sub_num, RoundMode dir)
                }
        }
 
-       framepos_t const ret_frame = frame_at_beat_locked (_metrics, beats + (ticks / BBT_Time::ticks_per_beat));
+       const framepos_t ret_frame = frame_at_beat_locked (_metrics, beats + (ticks / BBT_Time::ticks_per_beat));
 
        return ret_frame;
 }
 
-void
-TempoMap::round_bbt (BBT_Time& when, const int32_t& sub_num)
-{
-       if (sub_num == -1) {
-               const double bpb = meter_section_at (bbt_to_beats_locked (_metrics, when)).divisions_per_bar();
-               if ((double) when.beats > bpb / 2.0) {
-                       ++when.bars;
-               }
-               when.beats = 1;
-               when.ticks = 0;
-               return;
-       } else if (sub_num == 0) {
-               const double bpb = meter_section_at (bbt_to_beats_locked (_metrics, when)).divisions_per_bar();
-               if ((double) when.ticks > BBT_Time::ticks_per_beat / 2.0) {
-                       ++when.beats;
-                       while ((double) when.beats > bpb) {
-                               ++when.bars;
-                               when.beats -= (uint32_t) floor (bpb);
-                       }
-               }
-               when.ticks = 0;
-               return;
-       }
-       const uint32_t ticks_one_subdivisions_worth = BBT_Time::ticks_per_beat / sub_num;
-       double rem;
-       if ((rem = fmod ((double) when.ticks, (double) ticks_one_subdivisions_worth)) > (ticks_one_subdivisions_worth / 2.0)) {
-               /* closer to the next subdivision, so shift forward */
-
-               when.ticks = when.ticks + (ticks_one_subdivisions_worth - rem);
-
-               if (when.ticks > Timecode::BBT_Time::ticks_per_beat) {
-                       ++when.beats;
-                       when.ticks -= Timecode::BBT_Time::ticks_per_beat;
-               }
-
-       } else if (rem > 0) {
-               /* closer to previous subdivision, so shift backward */
-
-               if (rem > when.ticks) {
-                       if (when.beats == 0) {
-                               /* can't go backwards past zero, so ... */
-                       }
-                       /* step back to previous beat */
-                       --when.beats;
-                       when.ticks = Timecode::BBT_Time::ticks_per_beat - rem;
-               } else {
-                       when.ticks = when.ticks - rem;
-               }
-       }
-}
-
 framepos_t
 TempoMap::round_to_type (framepos_t frame, RoundMode dir, BBTPointType type)
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
 
-       double const beat_at_framepos = beat_at_frame_locked (_metrics, frame);
-       BBT_Time bbt (beats_to_bbt_locked (_metrics, beat_at_framepos));
+       const double beat_at_framepos = beat_at_frame_locked (_metrics, frame);
+       BBT_Time bbt (bbt_at_beat_locked (_metrics, beat_at_framepos));
 
        switch (type) {
        case Bar:
@@ -2544,22 +2795,22 @@ TempoMap::round_to_type (framepos_t frame, RoundMode dir, BBTPointType type)
                        /* find bar previous to 'frame' */
                        bbt.beats = 1;
                        bbt.ticks = 0;
-                       return frame_time (bbt);
+                       return frame_time_locked (_metrics, bbt);
 
                } else if (dir > 0) {
                        /* find bar following 'frame' */
                        ++bbt.bars;
                        bbt.beats = 1;
                        bbt.ticks = 0;
-                       return frame_time (bbt);
+                       return frame_time_locked (_metrics, bbt);
                } else {
                        /* true rounding: find nearest bar */
-                       framepos_t raw_ft = frame_time (bbt);
+                       framepos_t raw_ft = frame_time_locked (_metrics, bbt);
                        bbt.beats = 1;
                        bbt.ticks = 0;
-                       framepos_t prev_ft = frame_time (bbt);
+                       framepos_t prev_ft = frame_time_locked (_metrics, bbt);
                        ++bbt.bars;
-                       framepos_t next_ft = frame_time (bbt);
+                       framepos_t next_ft = frame_time_locked (_metrics, bbt);
 
                        if ((raw_ft - prev_ft) > (next_ft - prev_ft) / 2) { 
                                return next_ft;
@@ -2589,19 +2840,18 @@ TempoMap::get_grid (vector<TempoMap::BBTPoint>& points,
                    framepos_t lower, framepos_t upper)
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-       int32_t const upper_beat = (int32_t) ceil (beat_at_frame_locked (_metrics, upper));
-       int32_t cnt = floor (beat_at_frame_locked (_metrics, lower));
+       int32_t cnt = ceil (beat_at_frame_locked (_metrics, lower));
+       framecnt_t pos = 0;
        /* although the map handles negative beats, bbt doesn't. */
        if (cnt < 0.0) {
                cnt = 0.0;
        }
-       while (cnt <= upper_beat) {
-               framecnt_t pos = frame_at_beat_locked (_metrics, cnt);
-               TempoSection const tempo = tempo_section_at_locked (pos);
-               MeterSection const meter = meter_section_at_locked (pos);
-               BBT_Time const bbt = beats_to_bbt (cnt);
-
-               points.push_back (BBTPoint (meter, tempo_at_locked (pos), pos, bbt.bars, bbt.beats, tempo.get_c_func()));
+       while (pos < upper) {
+               pos = frame_at_beat_locked (_metrics, cnt);
+               const TempoSection tempo = tempo_section_at_locked (_metrics, pos);
+               const MeterSection meter = meter_section_at_locked (_metrics, pos);
+               const BBT_Time bbt = bbt_at_beat_locked (_metrics, cnt);
+               points.push_back (BBTPoint (meter, tempo_at_frame_locked (_metrics, pos), pos, bbt.bars, bbt.beats, tempo.c_func()));
                ++cnt;
        }
 }
@@ -2610,23 +2860,23 @@ const TempoSection&
 TempoMap::tempo_section_at (framepos_t frame) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-       return tempo_section_at_locked (frame);
+       return tempo_section_at_locked (_metrics, frame);
 }
 
 const TempoSection&
-TempoMap::tempo_section_at_locked (framepos_t frame) const
+TempoMap::tempo_section_at_locked (const Metrics& metrics, framepos_t frame) const
 {
        Metrics::const_iterator i;
        TempoSection* prev = 0;
 
-       for (i = _metrics.begin(); i != _metrics.end(); ++i) {
+       for (i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
 
                if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
                        if (!t->active()) {
                                continue;
                        }
-                       if (t->frame() > frame) {
+                       if (prev && t->frame() > frame) {
                                break;
                        }
 
@@ -2642,6 +2892,42 @@ TempoMap::tempo_section_at_locked (framepos_t frame) const
        return *prev;
 }
 
+const TempoSection&
+TempoMap::tempo_section_at_beat_locked (const Metrics& metrics, const double& beat) const
+{
+       TempoSection* prev_t = 0;
+       const MeterSection* prev_m = &meter_section_at_beat_locked (metrics, beat);
+
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               TempoSection* t;
+               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                       if (prev_t && ((t->pulse() - prev_m->pulse()) * prev_m->note_divisor()) + prev_m->beat() > beat) {
+                               break;
+                       }
+                       prev_t = t;
+               }
+
+       }
+       return *prev_t;
+}
+
+const TempoSection&
+TempoMap::tempo_section_at_pulse_locked (const Metrics& metrics, const double& pulse) const
+{
+       TempoSection* prev_t = 0;
+
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               TempoSection* t;
+               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                       if (prev_t && t->pulse() > pulse) {
+                               break;
+                       }
+                       prev_t = t;
+               }
+
+       }
+       return *prev_t;
+}
 
 /* don't use this to calculate length (the tempo is only correct for this frame).
    do that stuff based on the beat_at_frame and frame_at_beat api
@@ -2651,7 +2937,7 @@ TempoMap::frames_per_beat_at (const framepos_t& frame, const framecnt_t& sr) con
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
 
-       const TempoSection* ts_at = &tempo_section_at_locked (frame);
+       const TempoSection* ts_at = &tempo_section_at_locked (_metrics, frame);
        const TempoSection* ts_after = 0;
        Metrics::const_iterator i;
 
@@ -2676,101 +2962,133 @@ TempoMap::frames_per_beat_at (const framepos_t& frame, const framecnt_t& sr) con
        return ts_at->frames_per_beat (_frame_rate);
 }
 
-const Tempo
-TempoMap::tempo_at (const framepos_t& frame) const
+const MeterSection&
+TempoMap::meter_section_at_locked (const Metrics& metrics, framepos_t frame) const
 {
-       Glib::Threads::RWLock::ReaderLock lm (lock);
-       return tempo_at_locked (frame);
-}
+       Metrics::const_iterator i;
+       MeterSection* prev = 0;
 
-const Tempo
-TempoMap::tempo_at_locked (const framepos_t& frame) const
-{
-       TempoSection* prev_ts = 0;
+       for (i = metrics.begin(); i != metrics.end(); ++i) {
+               MeterSection* m;
 
-       Metrics::const_iterator i;
+               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
 
-       for (i = _metrics.begin(); i != _metrics.end(); ++i) {
-               TempoSection* t;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
-                       if (!t->active()) {
-                               continue;
-                       }
-                       if ((prev_ts) && t->frame() > frame) {
-                               /* t is the section past frame */
-                               double const ret = prev_ts->tempo_at_frame (frame, _frame_rate) * prev_ts->note_type();
-                               Tempo const ret_tempo (ret, prev_ts->note_type());
-                               return ret_tempo;
+                       if (prev && (*i)->frame() > frame) {
+                               break;
                        }
-                       prev_ts = t;
+
+                       prev = m;
                }
        }
 
-       double const ret = prev_ts->beats_per_minute();
-       Tempo const ret_tempo (ret, prev_ts->note_type ());
+       if (prev == 0) {
+               fatal << endmsg;
+               abort(); /*NOTREACHED*/
+       }
 
-       return ret_tempo;
+       return *prev;
 }
 
+
 const MeterSection&
 TempoMap::meter_section_at (framepos_t frame) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-       return meter_section_at_locked (frame);
+       return meter_section_at_locked (_metrics, frame);
 }
 
 const MeterSection&
-TempoMap::meter_section_at_locked (framepos_t frame) const
+TempoMap::meter_section_at_beat_locked (const Metrics& metrics, const double& beat) const
 {
-       //framepos_t const frame_off = frame + frame_offset_at (_metrics, frame);
-       Metrics::const_iterator i;
-       MeterSection* prev = 0;
+       MeterSection* prev_m = 0;
 
-       for (i = _metrics.begin(); i != _metrics.end(); ++i) {
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                MeterSection* m;
-
                if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-
-                       if (prev && (*i)->frame() > frame) {
+                       if (prev_m && m->beat() > beat) {
                                break;
                        }
-
-                       prev = m;
+                       prev_m = m;
                }
-       }
 
-       if (prev == 0) {
-               fatal << endmsg;
-               abort(); /*NOTREACHED*/
        }
+       return *prev_m;
+}
 
-       return *prev;
+const MeterSection&
+TempoMap::meter_section_at_beat (double beat) const
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       return meter_section_at_beat_locked (_metrics, beat);
 }
 
 const Meter&
-TempoMap::meter_at (framepos_t frame) const
+TempoMap::meter_at_frame (framepos_t frame) const
 {
        TempoMetric m (metric_at (frame));
        return m.meter();
 }
 
-const MeterSection&
-TempoMap::meter_section_at (const double& beat) const
+void
+TempoMap::fix_legacy_session ()
 {
-       MeterSection* prev_ms = 0;
-       Glib::Threads::RWLock::ReaderLock lm (lock);
+       MeterSection* prev_m = 0;
+       TempoSection* prev_t = 0;
 
-       for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
+       for (Metrics::iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
                MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-                       if (prev_ms && m->beat() > beat) {
-                               break;
+               TempoSection* t;
+
+               if ((m = dynamic_cast<MeterSection*>(*i)) != 0) {
+                       if (!m->movable()) {
+                               pair<double, BBT_Time> bbt = make_pair (0.0, BBT_Time (1, 1, 0));
+                               m->set_beat (bbt);
+                               m->set_pulse (0.0);
+                               m->set_frame (0);
+                               m->set_position_lock_style (AudioTime);
+                               prev_m = m;
+                               continue;
+                       }
+                       if (prev_m) {
+                               pair<double, BBT_Time> start = make_pair (((m->bbt().bars - 1) * prev_m->note_divisor())
+                                                                         + (m->bbt().beats - 1)
+                                                                         + (m->bbt().ticks / BBT_Time::ticks_per_beat)
+                                                                         , m->bbt());
+                               m->set_beat (start);
+                               const double start_beat = ((m->bbt().bars - 1) * prev_m->note_divisor())
+                                       + (m->bbt().beats - 1)
+                                       + (m->bbt().ticks / BBT_Time::ticks_per_beat);
+                               m->set_pulse (start_beat / prev_m->note_divisor());
+                       }
+                       prev_m = m;
+               } else if ((t = dynamic_cast<TempoSection*>(*i)) != 0) {
+
+                       if (!t->active()) {
+                               continue;
+                       }
+
+                       if (!t->movable()) {
+                               t->set_pulse (0.0);
+                               t->set_frame (0);
+                               t->set_position_lock_style (AudioTime);
+                               prev_t = t;
+                               continue;
                        }
-                       prev_ms = m;
-               }
 
+                       if (prev_t) {
+                               const double beat = ((t->legacy_bbt().bars - 1) * ((prev_m) ? prev_m->note_divisor() : 4.0))
+                                       + (t->legacy_bbt().beats - 1)
+                                       + (t->legacy_bbt().ticks / BBT_Time::ticks_per_beat);
+                               if (prev_m) {
+                                       t->set_pulse (beat / prev_m->note_divisor());
+                               } else {
+                                       /* really shouldn't happen but.. */
+                                       t->set_pulse (beat / 4.0);
+                               }
+                       }
+                       prev_t = t;
+               }
        }
-       return *prev_ms;
 }
 
 XMLNode&
@@ -2798,7 +3116,6 @@ TempoMap::set_state (const XMLNode& node, int /*version*/)
                XMLNodeList nlist;
                XMLNodeConstIterator niter;
                Metrics old_metrics (_metrics);
-               MeterSection* last_meter = 0;
                _metrics.clear();
 
                nlist = node.children();
@@ -2811,12 +3128,6 @@ TempoMap::set_state (const XMLNode& node, int /*version*/)
                                try {
                                        TempoSection* ts = new TempoSection (*child);
                                        _metrics.push_back (ts);
-
-                                       if (ts->bar_offset() < 0.0) {
-                                               if (last_meter) {
-                                                       //ts->update_bar_offset_from_bbt (*last_meter);
-                                               }
-                                       }
                                }
 
                                catch (failed_constructor& err){
@@ -2830,7 +3141,6 @@ TempoMap::set_state (const XMLNode& node, int /*version*/)
                                try {
                                        MeterSection* ms = new MeterSection (*child);
                                        _metrics.push_back (ms);
-                                       last_meter = ms;
                                }
 
                                catch (failed_constructor& err) {
@@ -2845,32 +3155,19 @@ TempoMap::set_state (const XMLNode& node, int /*version*/)
                        MetricSectionSorter cmp;
                        _metrics.sort (cmp);
                }
+
                /* check for legacy sessions where bbt was the base musical unit for tempo */
-               for (Metrics::iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
-                       MeterSection* m;
+               for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
                        TempoSection* t;
-                       MeterSection* prev_ms = 0;
-                       TempoSection* prev_ts = 0;
-                       if ((m = dynamic_cast<MeterSection*>(*i)) != 0) {
-                               if (prev_ms && prev_ms->pulse() < 0.0) {
-                                       /*XX we cannot possibly make this work??. */
-                                       pair<double, BBT_Time> start = make_pair (((prev_ms->bbt().bars - 1) * prev_ms->note_divisor()) + (prev_ms->bbt().beats - 1) + (prev_ms->bbt().ticks / BBT_Time::ticks_per_beat), prev_ms->bbt());
-                                       prev_ms->set_beat (start);
-                                       const double start_pulse = ((prev_ms->bbt().bars - 1) * prev_ms->note_divisor()) + (prev_ms->bbt().beats - 1) + (prev_ms->bbt().ticks / BBT_Time::ticks_per_beat);
-                                       prev_ms->set_pulse (start_pulse);
-                               }
-                               prev_ms = m;
-                       } else if ((t = dynamic_cast<TempoSection*>(*i)) != 0) {
-                               if (!t->active()) {
-                                       continue;
-                               }
-                               if (prev_ts && prev_ts->pulse() < 0.0) {
-                                       double const start = ((prev_ts->legacy_bbt().bars - 1) * prev_ms->note_divisor()) + (prev_ts->legacy_bbt().beats - 1) + (prev_ts->legacy_bbt().ticks / BBT_Time::ticks_per_beat);
-                                       prev_ts->set_pulse (start);
+                       if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                               if (t->legacy_bbt().bars != 0) {
+                                       fix_legacy_session();
+                                       break;
                                }
-                               prev_ts = t;
+                               break;
                        }
                }
+
                /* check for multiple tempo/meters at the same location, which
                   ardour2 somehow allowed.
                */
@@ -2879,19 +3176,19 @@ TempoMap::set_state (const XMLNode& node, int /*version*/)
                for (Metrics::iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
                        if (prev != _metrics.end()) {
                                MeterSection* ms;
-                               MeterSection* prev_ms;
+                               MeterSection* prev_m;
                                TempoSection* ts;
-                               TempoSection* prev_ts;
-                               if ((prev_ms = dynamic_cast<MeterSection*>(*prev)) != 0 && (ms = dynamic_cast<MeterSection*>(*i)) != 0) {
-                                       if (prev_ms->pulse() == ms->pulse()) {
-                                               cerr << string_compose (_("Multiple meter definitions found at %1"), prev_ms->pulse()) << endmsg;
-                                               error << string_compose (_("Multiple meter definitions found at %1"), prev_ms->pulse()) << endmsg;
+                               TempoSection* prev_t;
+                               if ((prev_m = dynamic_cast<MeterSection*>(*prev)) != 0 && (ms = dynamic_cast<MeterSection*>(*i)) != 0) {
+                                       if (prev_m->pulse() == ms->pulse()) {
+                                               cerr << string_compose (_("Multiple meter definitions found at %1"), prev_m->pulse()) << endmsg;
+                                               error << string_compose (_("Multiple meter definitions found at %1"), prev_m->pulse()) << endmsg;
                                                return -1;
                                        }
-                               } else if ((prev_ts = dynamic_cast<TempoSection*>(*prev)) != 0 && (ts = dynamic_cast<TempoSection*>(*i)) != 0) {
-                                       if (prev_ts->pulse() == ts->pulse()) {
-                                               cerr << string_compose (_("Multiple tempo definitions found at %1"), prev_ts->pulse()) << endmsg;
-                                               error << string_compose (_("Multiple tempo definitions found at %1"), prev_ts->pulse()) << endmsg;
+                               } else if ((prev_t = dynamic_cast<TempoSection*>(*prev)) != 0 && (ts = dynamic_cast<TempoSection*>(*i)) != 0) {
+                                       if (prev_t->pulse() == ts->pulse()) {
+                                               cerr << string_compose (_("Multiple tempo definitions found at %1"), prev_t->pulse()) << endmsg;
+                                               error << string_compose (_("Multiple tempo definitions found at %1"), prev_t->pulse()) << endmsg;
                                                return -1;
                                        }
                                }
@@ -2913,19 +3210,19 @@ TempoMap::dump (const Metrics& metrics, std::ostream& o) const
        Glib::Threads::RWLock::ReaderLock lm (lock, Glib::Threads::TRY_LOCK);
        const MeterSection* m;
        const TempoSection* t;
-       const TempoSection* prev_ts = 0;
+       const TempoSection* prev_t = 0;
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
 
                if ((t = dynamic_cast<const TempoSection*>(*i)) != 0) {
-                       o << "Tempo @ " << *i << " (Bar-offset: " << t->bar_offset() << ") " << t->beats_per_minute() << " BPM (pulse = 1/" << t->note_type() << ") at " << t->pulse() << " frame= " << t->frame() << " (movable? "
+                       o << "Tempo @ " << *i << t->beats_per_minute() << " BPM (pulse = 1/" << t->note_type() << ") at " << t->pulse() << " frame= " << t->frame() << " (movable? "
                          << t->movable() << ')' << " pos lock: " << enum_2_string (t->position_lock_style()) << std::endl;
                        o << "current      : " << t->beats_per_minute() << " | " << t->pulse() << " | " << t->frame() << std::endl;
-                       if (prev_ts) {
-                               o << "previous     : " << prev_ts->beats_per_minute() << " | " << prev_ts->pulse() << " | " << prev_ts->frame() << std::endl;
-                               o << "calculated   : " << prev_ts->tempo_at_pulse (t->pulse()) *  prev_ts->note_type() << " | " << prev_ts->pulse_at_tempo (t->pulses_per_minute(), t->frame(), _frame_rate) <<  " | " << prev_ts->frame_at_tempo (t->pulses_per_minute(), t->pulse(), _frame_rate) << std::endl;
+                       if (prev_t) {
+                               o << "previous     : " << prev_t->beats_per_minute() << " | " << prev_t->pulse() << " | " << prev_t->frame() << std::endl;
+                               o << "calculated   : " << prev_t->tempo_at_pulse (t->pulse()) *  prev_t->note_type() << " | " << prev_t->pulse_at_tempo (t->pulses_per_minute(), t->frame(), _frame_rate) <<  " | " << prev_t->frame_at_tempo (t->pulses_per_minute(), t->pulse(), _frame_rate) << std::endl;
                        }
-                       prev_ts = t;
+                       prev_t = t;
                } else if ((m = dynamic_cast<const MeterSection*>(*i)) != 0) {
                        o << "Meter @ " << *i << ' ' << m->divisions_per_bar() << '/' << m->note_divisor() << " at " << m->bbt() << " frame= " << m->frame()
                          << " pulse: " << m->pulse() <<  " beat : " << m->beat() << " pos lock: " << enum_2_string (m->position_lock_style()) << " (movable? " << m->movable() << ')' << endl;
@@ -3028,7 +3325,7 @@ TempoMap::insert_time (framepos_t where, framecnt_t amount)
                                                        continue;
                                                }
                                                const double beat = beat_at_pulse_locked (_metrics, t->pulse());
-                                               pair<double, BBT_Time> start = make_pair (beat, beats_to_bbt_locked (_metrics, beat));
+                                               pair<double, BBT_Time> start = make_pair (beat, bbt_at_beat_locked (_metrics, beat));
                                                ms->set_beat (start);
                                                ms->set_pulse (t->pulse());
                                        }
@@ -3173,7 +3470,7 @@ TempoMap::framepos_plus_bbt (framepos_t pos, BBT_Time op) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
 
-       BBT_Time pos_bbt = beats_to_bbt_locked (_metrics, beat_at_frame_locked (_metrics, pos));
+       BBT_Time pos_bbt = bbt_at_beat_locked (_metrics, beat_at_frame_locked (_metrics, pos));
        pos_bbt.ticks += op.ticks;
        if (pos_bbt.ticks >= BBT_Time::ticks_per_beat) {
                ++pos_bbt.beats;
@@ -3181,10 +3478,10 @@ TempoMap::framepos_plus_bbt (framepos_t pos, BBT_Time op) const
        }
        pos_bbt.beats += op.beats;
        /* the meter in effect will start on the bar */
-       double divisions_per_bar = meter_section_at (bbt_to_beats_locked (_metrics, BBT_Time (pos_bbt.bars + op.bars, 1, 0))).divisions_per_bar();
+       double divisions_per_bar = meter_section_at_beat (beat_at_bbt_locked (_metrics, BBT_Time (pos_bbt.bars + op.bars, 1, 0))).divisions_per_bar();
        while (pos_bbt.beats >= divisions_per_bar + 1) {
                ++pos_bbt.bars;
-               divisions_per_bar = meter_section_at (bbt_to_beats_locked (_metrics, BBT_Time (pos_bbt.bars + op.bars, 1, 0))).divisions_per_bar();
+               divisions_per_bar = meter_section_at_beat (beat_at_bbt_locked (_metrics, BBT_Time (pos_bbt.bars + op.bars, 1, 0))).divisions_per_bar();
                pos_bbt.beats -= divisions_per_bar;
        }
        pos_bbt.bars += op.bars;
@@ -3228,7 +3525,7 @@ operator<< (std::ostream& o, const MetricSection& section) {
        if ((ts = dynamic_cast<const TempoSection*> (&section)) != 0) {
                o << *((const Tempo*) ts);
        } else if ((ms = dynamic_cast<const MeterSection*> (&section)) != 0) {
-               //o << *((const Meter*) ms);
+               o << *((const Meter*) ms);
        }
 
        return o;