manual/xml/monitoring.xml

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   3 <!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [
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   5 ]>
   6
   7 <section id="sn-monitoring">
   8         <title>Monitoring</title>
   9         <para>
  10                 If you are recording an acoustic instrument or voice with no pre-existing
  11                 recorded material as an accompaniment, then you probably don't need to worry
  12                 about monitoring. Just make sure you've made the right
  13                 <link linkend="sn-jack">connections</link> and you should be ready to record
  14                 without reading this section.
  15         </para>
  16
  17         <para>
  18                 However, if a musician is playing an instrument (it doesn't matter what
  19                 kind) while listening to some pre-existing material, then it is important
  20                 that some mechanism exists to allow her to hear both her own playing and the
  21                 accompaniment. The same is true in a slightly different way if the
  22                 instrument makes no sound until the electrical signal it creates has been
  23                 amplified and fed to some loudspeakers. Listening to the performance in this
  24                 way is called monitoring.
  25         </para>
  26
  27         <para>
  28                 So, if you are recording an electrical or software instrument/signal, and/or
  29                 the musician wants to listen to existing material while performing, then you
  30                 need to ensure that signal routing is setup to allow monitoring. You have 2
  31                 basic choices:
  32         </para>
  33
  34         <section id="hardware-monitoring">
  35                 <title>Hardware Monitoring</title>
  36                 <para>
  37                         Hardware monitoring uses the capabilities of your audio interface to route
  38                         an incoming signal (e.g. someone playing a guitar into a microphone) to an
  39                         output connection (for example, the speaker outputs, or a dedicated analog
  40                         monitoring stereo pair). Most audio interfaces can do this, but how you get
  41                         them to do so, and what else they can do varies greatly. We can divide
  42                         audio interfaces into 3 general categories:
  43                 </para>
  44
  45                 <itemizedlist>
  46                         <listitem>
  47                                 <para>
  48                                         relatively simple, typically stereo, devices that allow the signal being
  49                                         recorded to be routed back to the main outputs (most "consumer" audio
  50                                         interfaces fit this description, along with anything that provides an
  51                                         "AC97-compliant CODEC")
  52                                 </para>
  53                         </listitem>
  54                         <listitem>
  55                                 <para>
  56                                         multichannel devices that allow a given input channel to be routed back
  57                                         to its corresponding output channel (the main example is the RME
  58                                         Digi9652)
  59                                 </para>
  60                         </listitem>
  61                         <listitem>
  62                                 <para>
  63                                         multichannel devices that allow any input channel, along with any
  64                                         playback channel, to be routed to any output channel (the RME HDSP and
  65                                         various interfaces based on the envy24/ice1712 chipsets, such as the
  66                                         M-Audio Delta 1010, EZ-8 and various Terratec cards)
  67                                 </para>
  68                         </listitem>
  69                 </itemizedlist>
  70
  71                 <section id="monitoring-consumer-audio-interfaces">
  72                         <title>"Consumer" audio interfaces and monitoring</title>
  73                         <para>
  74                                 For interfaces in the first category, there is no standard method of
  75                                 getting the signal routing correct. The variations in the wiring of
  76                                 hardware mixing chips, and the capabilities of those chips, means that you
  77                                 will have to get familiar with a hardware mixer control program and the
  78                                 details of your audio interface. In the simple cases, simply increasing
  79                                 the level named "Line In" or "Mic" in the hardware mixer control program
  80                                 will suffice. But this is not a general rule, because there is no general
  81                                 rule.
  82                         </para>
  83
  84                         <para>
  85                                 The following diagram shows a fairly typical AC97-based audio interface
  86                                 schematic:
  87                         </para>
  88                         <mediaobject>
  89                                 <imageobject>
  90                                         <imagedata fileref="images/simplemixer.png"/>
  91                                 </imageobject>
  92                         </mediaobject>
  93                         <para>
  94                                 Notice:
  95                         </para>
  96
  97                         <itemizedlist>
  98                                 <listitem>
  99                                         <para>
 100                                                 there are multiple input connections, but only one can be used as the
 101                                                 capture source
 102                                         </para>
 103                                 </listitem>
 104                                 <listitem>
 105                                         <para>
 106                                                 it is (normally) possible to route the input signals back to the
 107                                                 outputs, and independently control the gain for this "monitored" signal
 108                                         </para>
 109                                 </listitem>
 110                                 <listitem>
 111                                         <para>
 112                                                 it may or may not be possible to choose the playback stream as the
 113                                                 capture stream
 114                                         </para>
 115                                 </listitem>
 116                         </itemizedlist>
 117                 </section>
 118
 119                 <section id="monitoring-prosumer-audio-interfaces">
 120                         <title>High end "prosumer" interfaces and monitoring</title>
 121                         <para>
 122                                 For the only interface in the second category, the RME Digi9652
 123                                 ("Hammerfall"), the direct monitoring facilities are simplistic but useful
 124                                 in some circumstances. They are best controlled using <emphasis>JACK
 125                                 hardware monitoring</emphasis>.
 126                         </para>
 127
 128                         <para>
 129                                 When using one of the interfaces in the third category, most people find
 130                                 it useful to use hardware monitoring, but prefer to control it using a
 131                                 dedicated hardware mixer control program. If you have an RME HDSP system,
 132                                 then <command>hdspmixer</command> is the relevant program. For interfaces
 133                                 based on the envy24/ice1712/ice1724 chipsets, such as the Delta1010,
 134                                 Terratecs and others, <command>envy24ctl</command> is the right choice.
 135                                 Both programs offer access to very powerful matrix mixers that permit many
 136                                 different variations on signal routing, for both incoming signals and the
 137                                 signals being played back by the computer. You will need to spend some
 138                                 time working with these programs to grasp their potential and their usage
 139                                 in different situations.
 140                         </para>
 141
 142                         <para>
 143                                 The following diagram gives a partial view of the monitoring schemantics
 144                                 for this class of audio interface. Each input can be routed back to any
 145                                 output, and each such routing has its own gain control. The diagram only
 146                                 shows the routings for "in1" to avoid becoming completely
 147                                 incomprehensible.
 148                         </para>
 149                         <mediaobject>
 150                                 <imageobject>
 151                                         <imagedata fileref="images/matrixmixer.png"/>
 152                                 </imageobject>
 153                         </mediaobject>
 154                 </section>
 155         </section>
 156
 157         <section id="jack-hardware-monitoring">
 158                 <title>JACK hardware monitoring</title>
 159                 <para></para>
 160         </section>
 161
 162         <section id="software-monitoring">
 163                 <title>Software monitoring</title>
 164                 <para>
 165                         Much simpler than hardware monitoring is "software monitoring". This means
 166                         that any incoming signal (say, through a Line In connector) is delivered to
 167                         software (such as Ardour) which can then deliver it back to any output it
 168                         chooses, possibly having subjected it to various processing beforehand. The
 169                         software can also mix signals together before delivering them back to the
 170                         output. The fact that software monitoring can blend together incoming audio
 171                         with pre-recorded material while adjusting for latency and other factors is
 172                         the big plus for this method. The major downside is latency. There will
 173                         always be a delay between the signal arriving at your audio interface
 174                         inputs and it re-emerging from the outputs, and if this delay is too long,
 175                         it can cause problems for the performer who is listening. They will sense a
 176                         delay between pressing a key/pulling the bow/hitting the drum etc. and
 177                         hearing the sound it produces.
 178                 </para>
 179
 180                 <para>
 181                         However, if your system is capable of low latency audio, its likely that
 182                         you can use software monitoring effectively if it suits your goals.
 183                 </para>
 184         </section>
 185
 186         <section id="controlling-monitoring-within-ardour">
 187                 <title>Controlling monitoring choices within Ardour</title>
 188                 <para></para>
 189         </section>
 190 <!--
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 193         -->
 194 </section>