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I have an ALSA configuration that provides the following at the moment:

  • Take default audio and make it mono
  • Pass through alsaequal
  • Expand audio to 4 channels, all mono
  • Split 4 channels between 2 stereo sound cards

To get alsaequal to play nice with the 'type: multi' configuration, I had to pass through a configuration with the type 'asym' as recommended by someone, otherwise I'd get an error.

The configuration sort of works but I'm finding that a lot of the time, the audio is jittery at the very start of music tracks before playing normally. There's a lot going on in this configuration and I'm not 100% I've got it right. Have I done something wrong?

pcm.office-front {
    type hw
    card 0
    device 0
}
ctl.office-front {
    type hw
    card 0
}

pcm.office-back {
    type hw
    card 1
    device 0
}
ctl.office-back {
    type hw
    card 1
}

pcm.multi {
    type multi
    slaves.a.pcm "office-front"
    slaves.a.channels 2
    slaves.b.pcm "office-back"
    slaves.b.channels 2

    # office-front
    bindings.0.slave a
    bindings.0.channel 0    # bind alsa channel 0 to left
    bindings.1.slave a
    bindings.1.channel 1    # bind alsa channel 1 to left

    # office-back
    bindings.2.slave b
    bindings.2.channel 0    # bind alsa channel 2 to left
    bindings.3.slave b
    bindings.3.channel 1    # bind alsa channel 3 to left
}

pcm.duplex {
  type asym
  playback.pcm 20to40
  capture.pcm "hw:0,0"

}

pcm.20to40 {
  type route
  slave.channels 4;
  slave.pcm multi;
  ttable.0.0 1
  ttable.0.1 1
  ttable.0.2 1
  ttable.0.3 1
}

ctl.equal {
  type equal;
  controls "/home/pi/.alsaequal.bin"
}

pcm.plugequal {
  type equal;
  slave.pcm "plug:duplex";
  controls "/home/pi/.alsaequal.bin"
}

pcm.equal {
  type plug;
  slave.pcm plugequal;
}

pcm.!default {
  type route;
  slave.channels 2
  slave.pcm equal;
  ttable.1.0 1
  ttable.0.0 0.5
  ttable.0.1 0.5
}
  • What are the cards 0 and 1? – CL. Mar 7 '16 at 8:40
  • They are USB sound cards. Sabrent AU-MMSA – MrNorm Mar 7 '16 at 8:46

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