livetrax/manual/xml/monitoring.xml

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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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