root@CTZA:/home/fabio/Desktop/Download/mixxx-1.4.2# cat README.ALSA

ALSA support in Mixxx (alpha)
-----------------------------

Pre-requisites: A working ALSA setup - check the ALSA website[1] for
documentation and the Wiki[2] is also very helpful.

The ALSA support in Mixxx has been designed with a multichannel soundcard in
mind. However the flexibility of ALSA's plugin architecture allows other
audio hardware configurations to work with Mixxx.


1) multichannel card (4.0, 5.1, etc)
Test that the separate front and rear channels work using aplay, eg.

$ aplay -Dfront test.wav
$ aplay -Drear test.wav

or use James Courtier-Dutton's speaker-test utility[3].

By default, Mixxx uses the two plugins: the plug plugin to convert sampling
rate, format, etc and the surround40 plugin to pipe the audio stream to the
correct channels. If the above tests work then Mixxx should work once you
have placed the following stanza in your ~/.asoundrc file.

pcm.mixxx {
  type           plug
  slave.pcm      "surround40:0"
  slave.channels 4
}


2) single stereo card
One possible way to use a stereo card for mixing is to combine the master
channels to the left output and the headphone (pre-listen) channels to the
right output.

pcm.mixxx {
  type           route
  slave.pcm      "hw:0"
  slave.channels 2
  ttable.0.0     0.5
  ttable.1.0     0.5
  ttable.2.1     0.5
  ttable.3.1     0.5
}


3) 2 or more stereo cards
Tie together two sound cards using the multi plugin. The output from the
first card (hw:0) is the master output and the second card (hw:1) serves as
the headphone output.

pcm.mixxxmulti {
        type multi
        slaves.a.pcm "hw:0"
        slaves.a.channels 2
        slaves.b.pcm "hw:1"
        slaves.b.channels 2
        bindings.0.slave a
        bindings.0.channel 0
        bindings.1.slave a
        bindings.1.channel 1
        bindings.2.slave b
        bindings.2.channel 0
        bindings.3.slave b
        bindings.3.channel 1
}

pcm.mixxx {
        type route
        slave.pcm "mixxxmulti"
        ttable.0.0 1
        ttable.1.1 1
        ttable.2.2 1
        ttable.3.3 1
}


NB why doesn't the plug plugin work in place of the route plugin in the last
two configurations?

[1] http://www.alsa-project.org
[2] http://alsa.opensrc.org/
[3] http://www.superbug.demon.co.uk/speaker-test/