====== alsa 4 sorties avec 2 cartes USB ======

mettre dans .asoundrc
<code>
# Utilise card "les2" par defaut a travers le plugin "plug"
# converti automatiquement channels, rate et format.
pcm.!default {
  type plug
  slave {
    pcm "les2"
    rate 44100
    channels 2
  }
}

ctl.!default {
  type hw
  card "CODEC"
}

pcm.usb1 {
  type hw
  card "CODEC"
  channels 2
  rate 44100
}

ctl.usb1 {
  type hw
  card "CODEC"
}

pcm.usb2 {
  type hw
  card "Device"
  channels 2
  rate 44100
}

ctl.usb2 {
  type hw
  card "Device"
}

# Creer card "les2", wrapper autour du plugin : "route".
pcm.les2 {
  # The "route" plugin routes channels from its input card to its output.
  type route

  # Slave is the input card.
  slave {
    # The virtual input card has 4 channels. Yes, this is circumstantial and
    # also must be specified explicitly.
    channels 4

    # Unnamed definition of the input card.
    pcm {
      # The "les2" plugin merges several cards into one. This is necessary,
      # because the "route" plugin can only handle one card.
      type multi
  
      # Definition of the child cards.
      slaves {
        # Definition of child card "a".
        a {
          pcm {
            type dmix
            ipc_key 1024
            slave.pcm "usb1"
          }
          channels 2
        }
        b {
          pcm {
            type dmix
            ipc_key 2048
            slave.pcm "usb2"
          }
          channels 2
        }
      }

      # Definition of the card's channels.
      bindings {
        # Channel 0...
        0 {
          # ... bound to child card "a"'s...
          slave a
          # ... channel 0.
          channel 0
        }
        1 {
          slave a
          channel 1
        }
        2 {
          slave b
          channel 0
        }
        3 {
          slave b
          channel 1
        }
      }
    }
  }
  ttable {
    # Channel 0...
    0 {
      # ... bound to child card's channel 0 at full volume...
      0 1.0
      # ... AND child child card's channel 1 at full volume.
      1 1.0
    }
    1 {
      2 1.0
      3 1.0
    }
  }
}


</code>