/* LTC signal should have a rise time of 25 us +/- 5 us.
* yet with most sound-cards a square-wave of 1-2 sample
- * introduces rather some ringing and small oscillations.
- * so we low-pass filter the signal a bit, depending
- * on the sample-rate.
+ * introduces ringing and small oscillations.
+ * https://en.wikipedia.org/wiki/Gibbs_phenomenon
+ * A low-pass filter in libltc can reduce this at
+ * the cost of being slightly out of spec WRT to rise-time.
*
- * TODO: this should become an adaptive value, when
- * the playback speed is increases so that 1 bit < 3-4
- * audio samples, we should fall back to 25 us.
+ * This filter is adaptive so that fast vari-speed signals
+ * will not be affected by it.
*/
-#define LTC_RISE_TIME MIN (100, MAX(25, (2000000 / engine().frame_rate())))
+#define LTC_RISE_TIME(speed) MIN (100, MAX(40, (4000000 / ((speed==0)?1:speed) / engine().frame_rate())))
+
+#define TV_STANDARD(tcf) \
+ (timecode_to_frames_per_second(tcf)==25.0 ? LTC_TV_625_50 : \
+ timecode_has_drop_frames(tcf)? LTC_TV_525_60 : LTC_TV_FILM_24)
void
Session::ltc_tx_initialize()
{
ltc_enc_tcformat = config.get_timecode_format();
+ ltc_tx_parse_offset();
DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX init sr: %1 fps: %2\n", nominal_frame_rate(), timecode_to_frames_per_second(ltc_enc_tcformat)));
ltc_encoder = ltc_encoder_create(nominal_frame_rate(),
timecode_to_frames_per_second(ltc_enc_tcformat),
- 0);
+ TV_STANDARD(ltc_enc_tcformat), 0);
ltc_encoder_set_bufsize(ltc_encoder, nominal_frame_rate(), 23.0);
- ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME);
+ ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(1.0));
/* buffersize for 1 LTC frame: (1 + sample-rate / fps) bytes
* usually returned by ltc_encoder_get_buffersize(encoder)
ltc_tx_resync_latency();
Xrun.connect_same_thread (*this, boost::bind (&Session::ltc_tx_reset, this));
engine().GraphReordered.connect_same_thread (*this, boost::bind (&Session::ltc_tx_resync_latency, this));
+ restarting = false;
}
void
Session::ltc_tx_cleanup()
{
DEBUG_TRACE (DEBUG::LTC, "LTC TX cleanup\n");
- if (ltc_enc_buf) free(ltc_enc_buf);
+ free(ltc_enc_buf);
+ ltc_enc_buf = NULL;
ltc_encoder_free(ltc_encoder);
ltc_encoder = NULL;
}
ltc_buf_off = 0;
ltc_enc_byte = 0;
ltc_enc_cnt = 0;
+
+ ltc_encoder_reset(ltc_encoder);
+}
+
+void
+Session::ltc_tx_parse_offset() {
+ Timecode::Time offset_tc;
+ Timecode::parse_timecode_format(config.get_timecode_generator_offset(), offset_tc);
+ offset_tc.rate = timecode_frames_per_second();
+ offset_tc.drop = timecode_drop_frames();
+ timecode_to_sample(offset_tc, ltc_timecode_offset, false, false);
+ ltc_timecode_negative_offset = !offset_tc.negative;
}
void
a3tc.drop = timecode_has_drop_frames(ltc_enc_tcformat);
Timecode::timecode_to_sample (a3tc, ltc_enc_pos, true, false,
- double(frame_rate()),
+ (double)frame_rate(),
config.get_subframes_per_frame(),
- config.get_timecode_offset_negative(), config.get_timecode_offset()
+ ltc_timecode_negative_offset, ltc_timecode_offset
);
+ restarting = false;
}
void
TimecodeFormat cur_timecode = config.get_timecode_format();
if (cur_timecode != ltc_enc_tcformat) {
DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX1: TC format mismatch - reinit sr: %1 fps: %2\n", nominal_frame_rate(), timecode_to_frames_per_second(cur_timecode)));
- if (ltc_encoder_reinit(ltc_encoder, nominal_frame_rate(), timecode_to_frames_per_second(cur_timecode), 0)) {
+ if (ltc_encoder_reinit(ltc_encoder, nominal_frame_rate(),
+ timecode_to_frames_per_second(cur_timecode),
+ TV_STANDARD(cur_timecode), 0
+ )) {
PBD::error << _("LTC encoder: invalid framerate - LTC encoding is disabled for the remainder of this session.") << endmsg;
ltc_tx_cleanup();
return;
}
- if (nominal_frame_rate() <= 48000) {
- ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME);
- }
+ ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(ltc_speed));
ltc_enc_tcformat = cur_timecode;
+ ltc_tx_parse_offset();
ltc_tx_reset();
}
*/
framepos_t cycle_start_frame = (current_speed < 0) ? (start_frame - ltc_out_latency.max) : (start_frame + ltc_out_latency.max);
+ /* LTC TV standard offset */
+ cycle_start_frame -= ltc_frame_alignment(frames_per_timecode_frame(), TV_STANDARD(cur_timecode));
+
/* cycle-start may become negative due to latency compensation */
if (cycle_start_frame < 0) { cycle_start_frame = 0; }
- double new_ltc_speed = double(labs(end_frame - start_frame) * SIGNUM(current_speed)) / double(nframes);
+ double new_ltc_speed = (double)(labs(end_frame - start_frame) * SIGNUM(current_speed)) / (double)nframes;
+ if (nominal_frame_rate() != frame_rate()) {
+ new_ltc_speed *= (double)nominal_frame_rate() / (double)frame_rate();
+ }
if (SIGNUM(new_ltc_speed) != SIGNUM (ltc_speed)) {
DEBUG_TRACE (DEBUG::LTC, "LTC TX2: transport changed direction\n");
*/
DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: speed change old: %1 cur: %2 tgt: %3 ctd: %4\n", ltc_speed, current_speed, target_speed, fabs(current_speed) - target_speed));
speed_changed = true;
+ ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(new_ltc_speed));
}
if (end_frame == start_frame || fabs(current_speed) < 0.1 ) {
* which is left for later..
*/
- double oldbuflen = double(ltc_buf_len - ltc_buf_off);
- double newbuflen = double(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
+ double oldbuflen = (double)(ltc_buf_len - ltc_buf_off);
+ double newbuflen = (double)(ltc_buf_len - ltc_buf_off) * fabs(ltc_speed / new_ltc_speed);
DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: bufOld %1 bufNew %2 | diff %3\n",
(ltc_buf_len - ltc_buf_off), newbuflen, newbuflen - oldbuflen
framepos_t tc_sample_start;
/* calc timecode frame from current position - round down to nearest timecode */
- sample_to_timecode(cycle_start_frame, tc_start, true, false);
+ Timecode::sample_to_timecode(cycle_start_frame, tc_start, true, false,
+ timecode_frames_per_second(),
+ timecode_drop_frames(),
+ (double)frame_rate(),
+ config.get_subframes_per_frame(),
+ ltc_timecode_negative_offset, ltc_timecode_offset
+ );
/* convert timecode back to sample-position */
Timecode::timecode_to_sample (tc_start, tc_sample_start, true, false,
- double(frame_rate()),
+ (double)frame_rate(),
config.get_subframes_per_frame(),
- config.get_timecode_offset_negative(), config.get_timecode_offset()
+ ltc_timecode_negative_offset, ltc_timecode_offset
);
/* difference between current frame and TC frame in samples */
maxdiff = slave()->resolution();
} else {
maxdiff = ceil(fabs(ltc_speed))*2.0;
+ if (nominal_frame_rate() != frame_rate()) {
+ maxdiff *= 3.0;
+ }
+ if (ltc_enc_tcformat == Timecode::timecode_23976 || ltc_enc_tcformat == Timecode::timecode_24976) {
+ maxdiff *= 15.0;
+ }
}
DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX4: enc: %1 + %2 - %3 || buf-bytes: %4 enc-byte: %5\n",
rint(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame
));
- if (ltc_speed != 0 && fabs(ceil(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) > maxdiff) {
+ if (ltc_enc_pos < 0
+ || (ltc_speed != 0 && fabs(ceil(ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) > maxdiff)
+ ) {
// (5) re-align
ltc_tx_reset();
if (ltc_speed < 0 ) {
/* calculate the byte that starts at or after the current position */
ltc_enc_byte = floor((10.0 * soff) / (fptcf));
- ltc_enc_cnt = double(ltc_enc_byte * fptcf / 10.0);
+ ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
/* calculate difference between the current position and the byte to send */
cyc_off = soff- ceil(ltc_enc_cnt);
} else {
/* calculate the byte that starts at or after the current position */
ltc_enc_byte = ceil((10.0 * soff) / fptcf);
- ltc_enc_cnt = double(ltc_enc_byte * fptcf / 10.0);
+ ltc_enc_cnt = ltc_enc_byte * fptcf / 10.0;
/* calculate difference between the current position and the byte to send */
cyc_off = ceil(ltc_enc_cnt) - soff;
DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart encoder: soff %1 byte %2 cycoff %3\n",
soff, ltc_enc_byte, cyc_off));
+ if ( (ltc_speed < 0 && ltc_enc_byte !=9 ) || (ltc_speed >= 0 && ltc_enc_byte !=0 ) ) {
+ restarting = true;
+ }
+
if (cyc_off > 0 && cyc_off <= nframes) {
/* offset in this cycle */
txf= rint(cyc_off / fabs(ltc_speed));
DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 | byte %4\n",
ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
}
-#if 1 /* experimental sample bit alignment */
else if (ltc_speed != 0 && (fptcf / ltc_speed / 80) > 3 ) {
- /* We may get away without a DLL if speed-changes are uniform enough and
- * no oscillation takes place, the linear approx here should reduce the
- * jitter sufficiently when generating LTC from another LTC source or
- * JACK-transport or ardour internal clock.
- *
- * Note that the granularity of the LTC encoder speed is 1 byte =
+ /* reduce (low freq) jitter.
+ * The granularity of the LTC encoder speed is 1 byte =
* (frames-per-timecode-frame / 10) audio-samples.
+ * Thus, tiny speed changes [as produced by some slaves]
+ * may not have any effect in the cycle when they occur,
+ * but they will add up over time.
+ *
+ * This is a linear approx to compensate for this jitter
+ * and prempt re-sync when the drift builds up.
+ *
+ * However, for very fast speeds - when 1 LTC bit is
+ * <= 3 audio-sample - adjusting speed may lead to
+ * invalid frames.
*
- * Thus, tiny speed changes won't have any effect and larger ones
- * may lead to oscillations.
- * To be better than that, resampling (or a rewrite of the encoder) is
- * required.
+ * To do better than this, resampling (or a rewrite of the
+ * encoder) is required.
*/
ltc_speed -= ((ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) / engine().frame_rate();
}
-#endif
// (6) encode and output
}
}
- if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
- DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoder error byte %1\n", ltc_enc_byte));
- ltc_encoder_buffer_flush(ltc_encoder);
- ltc_tx_reset();
- return;
+ int enc_frames;
+
+ if (restarting) {
+ /* write zero bytes -- don't touch encoder until we're at a frame-boundary
+ * otherwise the biphase polarity may be inverted.
+ */
+ enc_frames = fptcf / 10.0;
+ memset(<c_enc_buf[ltc_buf_len], 127, enc_frames * sizeof(ltcsnd_sample_t));
+ } else {
+ if (ltc_encoder_encode_byte(ltc_encoder, ltc_enc_byte, (ltc_speed==0)?1.0:(1.0/ltc_speed))) {
+ DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoder error byte %1\n", ltc_enc_byte));
+ ltc_encoder_buffer_flush(ltc_encoder);
+ ltc_tx_reset();
+ return;
+ }
+ enc_frames = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
}
- int enc_frames = ltc_encoder_get_buffer(ltc_encoder, &(ltc_enc_buf[ltc_buf_len]));
+
#ifdef LTC_GEN_FRAMEDBUG
DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX6.3 encoded %1 bytes for LTC-byte %2 at spd %3\n", enc_frames, ltc_enc_byte, ltc_speed));
#endif
ltc_enc_cnt = 0;
} else if (ltc_enc_byte == 0) {
ltc_enc_cnt = 0;
+ restarting=false;
}
}
#ifdef LTC_GEN_FRAMEDBUG
projects / ardour.git / blobdiff