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livetrax/manual/xml/jack.xml
Paul Davis 45d3ec1437 merged with 1697 revision of trunk (which is post-rc1 but pre-rc2
git-svn-id: svn://localhost/ardour2/branches/2.1-staging@1698 d708f5d6-7413-0410-9779-e7cbd77b26cf
2007-04-11 13:07:51 +00:00

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<?xml version="1.0" standalone="no"?>
<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [
]>
<section id="sn-configuring-jack">
<title>Getting Audio In, Out and Around Your Computer</title>
<para>
Before you can begin to use Ardour, you will need to get the audio
input/output capabilities of your system working and properly
configured. There are two aspects to this process: getting your audio
interface (soundcard) working, and configuring it to work with the Jack
Audio Connection Kit (<ulink url="http://jackaudio.org/">JACK</ulink>).
</para>
<section id="sn-jack">
<title>JACK</title>
<para>
It is extremely important to understand that Ardour does not interact
directly with your audio interface when it is running. Instead, all of
the audio data signals that Ardour receives and generates are sent to
and from JACK, a piece of software that routes audio data between an
audio interface and audio applications, in real time.
</para>
<para>
Traditionally, most of the audio sources that you would want to
record, as well as a lot of the more significant effects processing,
existed outside the computer. Consequently one of the biggest issues
in integrating a computer into the operation of the studio is how to
move audio data in and out of the computer.
</para>
<para>
However, it is becoming increasingly common for studios to use audio
sources and effects processing that are comprised completely of
software, quite often running on the same machine as an audio
sequencer or digital audio workstation (DAW). A new problem arises in
such situations, because moving audio in and out of the DAW no longer
involves your hardware audio interface. Instead, data has to be moved
from one piece of software to another, preferably with the same kind
of sample synchronisation youd have in a properly configured
digital hardware system. This is a problem that has been solved at
least a couple of times (ReWire from PropellerHeads and DirectConnect
from Digidesign are the two most common examples), but JACK is a new
design developed as an open source software project, and is thusly
available for anyone to use, learn from, extend, *fix or modify.
</para>
<para>
New users may not initially realize that by using Jack, their computer
becomes an extremely flexible and powerful audio tool - especially
with Ardour acting as the heart of the system.
</para>
</section>
<section id="getting-audio-working">
<title>Getting Your Audio Interface Working</title>
<note>
<para>
Although Ardour runs on OS X as well as Linux, this documentation
describes only a Linux (ALSA) system. The issues faced on OS X tend
to be entirely different, and are centered mostly on JACK. There are
also alternative audio device driver families for Linux but they are
also not discussed here.
</para>
</note>
<para>
Getting your audio interface working can be the hardest part of
setting your computer up to run Ardour, or it could be one of the
easiest. The level of difficulty you will face depends on the type of
audio interface ("soundcard") you are using, the operating system
version you are using, and your own understanding of how it all works.
</para>
<para>
In an ideal world, your computer already has a working audio
interface, and all you need do is to start up qjackctl and run JACK.
You can determine if you face this ideal situation by doing a few
simple tests on your machine. The most obvious test is whether
youve already heard audio coming out of your computer. If you are
in this situation, you can skip ahead to
<xref linkend="selecting-capture-source"/>.
</para>
</section>
<section id="checking-for-an-audio-interface">
<title>Checking For an Audio Interface</title>
<para>
If youve never tried to play audio on your computer before, you
should use a basic playback program such as play, aplay or possibly
xmms. Find an audio file on your machine (<command>locate
.wav</command> may help here), and try to play it. There are several
possibilities:
</para>
<itemizedlist>
<listitem>
<para>
You may get an error from the program
</para>
</listitem>
<listitem>
<para>
You may hear nothing
</para>
</listitem>
<listitem>
<para>
You may hear something, but its too quiet
</para>
</listitem>
<listitem>
<para>
you may hear something from the wrong loudspeakers.
</para>
</listitem>
</itemizedlist>
</section>
<section id="selecting-capture-source">
<title>Selecting Capture Source</title>
<para>
Many audio interfaces, particularly the cheaper varieties that are
often found built into computers, have ways to plug in both
microphones and instruments or other audio equipment to be recorded.
This immediately poses a question: how does Ardour (or any software)
know which signal to record, the one coming into the microphone input,
or the one arriving at the "line in" socket? The same question arises
also for "high-end" audio interfaces, though in different ways.
</para>
<para>
The short answer is: Ardour doesnt. Instead, this is a choice you
have to make using a program a program that understands how to control
the mixing hardware on the audio interface. Linux/ALSA has a number of
such programs: alsamixer, gamix, aumix, kmix are just a few of them.
Each of them offers you a way to select which of the possible
recordable signals will be used for as the "capture source". How you
select the preferred signal varies from program to program, so you
will have to consult the help documentation for whichever program you
choose to use.
</para>
<para>
There are also a few programs that offer ways to control just one
particular kind of audio interface. For example, the
<application>hdspmixer</application> program offers control over the
very powerful matrix mixer present on several RME audio interface.
<application>envy24ctrl</application> does the same for a number of
interfaces built around the common ice1712/envy24 chipset, found in
devices from M-Audio, Terratec and others. Please note that this quite
similar to the situation for Windows and MacOS users, where each audio
interface often comes with its own control program that allows certain
critical configuration choices to be made.
</para>
<section id="problems-with-input-signal">
<title>"I dont get any signal when I record …"</title>
<para>
The most common problem for first-time audio users on Linux is to
try to record something and get no signal at all, or alternatively,
a very low signal. The low signal problem typically arises from one
or more of the following issues:
</para>
<itemizedlist>
<listitem>
<para>
a microphone input plugged into the "line in" socket of the
interface. The signal levels delivered by microphones are very
small, and require amplification before they can be used by most
audio circuitry. In professional recording studios, this is done
using a dedicated box called a "pre-amplifier". If your audio
interface has a "mic input" socket, then it has its own
pre-amplifier built in, although its probably not a very good
one. If you make the mistake of plugging a microphone into the
"line in" socket, you will get either an inaudible or very quiet
signal.
</para>
</listitem>
<listitem>
<para>
the wrong capture source selected in the audio interfaces
hardware mixer (see above)
</para>
</listitem>
<listitem>
<para>
the "capture" gain level in the audio interfaces hardware
mixer is turned down too low. You will need to use a hardware
mixer application (as described above) to increase this.
</para>
</listitem>
</itemizedlist>
<note>
<para>
You will notice in the mixer strip for each track in ardour that
you can change the selection of the monitoring source between
input/pre/post. Adjusting the fader while watching the input
levels will NOT have any affect on the levels. As mentioned above,
ardour is dependent on external mixer settings for a source level.
</para>
</note>
</section>
</section>
<section id="monitoring-choices">
<title>Monitoring Choices</title>
<para>
Its unfortunate that we have to raise this issue at a point in the
manual where you, the reader, may not even knoiw what "monitoring"
means. However, it is such an absolutely critical aspect of using any
digital audio workstation that we need to at least cover the basics
here. The only people who dont need to care about monitoring are
those who will never use ardour to record a live performance (even on
performed using a software synthesizer).
</para>
<para>
Monitoring is the term we use to describe listening to what ardour is
recording. If you are playing a guitar and recording it with ardour,
you can probably hear the guitars own sound, but there are many
situations where relying on the sound of the instrument is completely
inadequate. For example, with an electronic instrument, there is no
sound until the electrical signal that it generates has been processed
by an amplifier and fed to a loudspeaker. But if Ardour is recording
the instruments signal, what is responsible for sending it to the
amp+loudspeakers? It can get a lot more complex than that: if you are
recording multiple performers at the same time, each performer needs
to hear their own playing/singing, but they also probably need to hear
some of their colleagues sound as well. You might be overdubbing
yourself - playing a new line on an instrument while listening to
tracks youve already recorded - how do you hear the new material as
well as the existing stuff?
</para>
<para>
Well, hopefully, youre convinced that there are some questions to
be dealt with surrounding monitoring, see
<xref linkend="sn-monitoring"/> for more in depth information.
</para>
</section>
<section id="using-multiple-soundcards">
<title>Can I use multiple soundcards</title>
<para>
There are really lots of great reasons why you should not even attempt
to do this. But seriously, save your money for a while and buy
yourself a properly designed multichannel soundcard.
</para>
</section>
<section id="qjackctl">
<title>Qjackctl</title>
<para>
JACK itself does not come with graphical user interface - to start
JACK and control it you need to have access to a command line and a
basic knowledge of Unix-like operating systems. However,
<ulink url="http://qjackctl.sourceforge.net/">qjackctl</ulink> is a
wonderful application that wraps JACK up with a graphical interface
that is both nice to look at and useful at same time. qjackctl is the
recommended way of using JACK.
</para>
<mediaobject>
<imageobject>
<imagedata fileref="images/qjackctl.png"/>
</imageobject>
</mediaobject>
<para>
You should be able to start qjackctl from the “application menu”
of your system, typically found on the panel/appbar/dock or whatever
its called that lives at the top/bottom/left/right of your screen.
</para>
<para>
[ need screenshot of GNOME/KDE/OSX menus here ]
</para>
</section>
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