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]>
<section id="sn-monitoring">
<title>Monitoring</title>
<para>
If you are recording an acoustic instrument or voice with no pre-existing
recorded material as an accompaniment, then you probably don't need to worry
about monitoring. Just make sure you've made the right
<link linkend="sn-jack">connections</link> and you should be ready to record
without reading this section.
</para>
<para>
However, if a musician is playing an instrument (it doesn't matter what
kind) while listening to some pre-existing material, then it is important
that some mechanism exists to allow her to hear both her own playing and the
accompaniment. The same is true in a slightly different way if the
instrument makes no sound until the electrical signal it creates has been
amplified and fed to some loudspeakers. Listening to the performance in this
way is called monitoring.
</para>
<para>
So, if you are recording an electrical or software instrument/signal, and/or
the musician wants to listen to existing material while performing, then you
need to ensure that signal routing is setup to allow monitoring. You have 2
basic choices:
</para>
<section id="hardware-monitoring">
<title>Hardware Monitoring</title>
<para>
Hardware monitoring uses the capabilities of your audio interface to route
an incoming signal (e.g. someone playing a guitar into a microphone) to an
output connection (for example, the speaker outputs, or a dedicated analog
monitoring stereo pair). Most audio interfaces can do this, but how you get
them to do so, and what else they can do varies greatly. We can divide
audio interfaces into 3 general categories:
</para>
<itemizedlist>
<listitem>
<para>
relatively simple, typically stereo, devices that allow the signal being
recorded to be routed back to the main outputs (most "consumer" audio
interfaces fit this description, along with anything that provides an
"AC97-compliant CODEC")
</para>
</listitem>
<listitem>
<para>
multichannel devices that allow a given input channel to be routed back
to its corresponding output channel (the main example is the RME
Digi9652)
</para>
</listitem>
<listitem>
<para>
multichannel devices that allow any input channel, along with any
playback channel, to be routed to any output channel (the RME HDSP and
various interfaces based on the envy24/ice1712 chipsets, such as the
M-Audio Delta 1010, EZ-8 and various Terratec cards)
</para>
</listitem>
</itemizedlist>
<section id="monitoring-consumer-audio-interfaces">
<title>"Consumer" audio interfaces and monitoring</title>
<para>
For interfaces in the first category, there is no standard method of
getting the signal routing correct. The variations in the wiring of
hardware mixing chips, and the capabilities of those chips, means that you
will have to get familiar with a hardware mixer control program and the
details of your audio interface. In the simple cases, simply increasing
the level named "Line In" or "Mic" in the hardware mixer control program
will suffice. But this is not a general rule, because there is no general
rule.
</para>
<para>
The following diagram shows a fairly typical AC97-based audio interface
schematic:
</para>
<mediaobject>
<imageobject>
<imagedata fileref="images/simplemixer.png"/>
</imageobject>
</mediaobject>
<para>
Notice:
</para>
<itemizedlist>
<listitem>
<para>
there are multiple input connections, but only one can be used as the
capture source
</para>
</listitem>
<listitem>
<para>
it is (normally) possible to route the input signals back to the
outputs, and independently control the gain for this "monitored" signal
</para>
</listitem>
<listitem>
<para>
it may or may not be possible to choose the playback stream as the
capture stream
</para>
</listitem>
</itemizedlist>
</section>
<section id="monitoring-prosumer-audio-interfaces">
<title>High end "prosumer" interfaces and monitoring</title>
<para>
For the only interface in the second category, the RME Digi9652
("Hammerfall"), the direct monitoring facilities are simplistic but useful
in some circumstances. They are best controlled using <emphasis>JACK
hardware monitoring</emphasis>.
</para>
<para>
When using one of the interfaces in the third category, most people find
it useful to use hardware monitoring, but prefer to control it using a
dedicated hardware mixer control program. If you have an RME HDSP system,
then <command>hdspmixer</command> is the relevant program. For interfaces
based on the envy24/ice1712/ice1724 chipsets, such as the Delta1010,
Terratecs and others, <command>envy24ctl</command> is the right choice.
Both programs offer access to very powerful matrix mixers that permit many
different variations on signal routing, for both incoming signals and the
signals being played back by the computer. You will need to spend some
time working with these programs to grasp their potential and their usage
in different situations.
</para>
<para>
The following diagram gives a partial view of the monitoring schemantics
for this class of audio interface. Each input can be routed back to any
output, and each such routing has its own gain control. The diagram only
shows the routings for "in1" to avoid becoming completely
incomprehensible.
</para>
<mediaobject>
<imageobject>
<imagedata fileref="images/matrixmixer.png"/>
</imageobject>
</mediaobject>
</section>
</section>
<section id="jack-hardware-monitoring">
<title>JACK hardware monitoring</title>
<para></para>
</section>
<section id="software-monitoring">
<title>Software monitoring</title>
<para>
Much simpler than hardware monitoring is "software monitoring". This means
that any incoming signal (say, through a Line In connector) is delivered to
software (such as Ardour) which can then deliver it back to any output it
chooses, possibly having subjected it to various processing beforehand. The
software can also mix signals together before delivering them back to the
output. The fact that software monitoring can blend together incoming audio
with pre-recorded material while adjusting for latency and other factors is
the big plus for this method. The major downside is latency. There will
always be a delay between the signal arriving at your audio interface
inputs and it re-emerging from the outputs, and if this delay is too long,
it can cause problems for the performer who is listening. They will sense a
delay between pressing a key/pulling the bow/hitting the drum etc. and
hearing the sound it produces.
</para>
<para>
However, if your system is capable of low latency audio, its likely that
you can use software monitoring effectively if it suits your goals.
</para>
</section>
<section id="controlling-monitoring-within-ardour">
<title>Controlling monitoring choices within Ardour</title>
<para></para>
</section>
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