BallonSonde/sysconfig/alsa/conf.d/50_aec.conf

### ALSA virtual device which combines recording and playback loopback for AEC processing
# https://github.com/sanebow/alsa-aec
# sanebow@gmail.com
# Version: 0.3 (20210506)

defaults.pcm.aec.playback_hw.card defaults.pcm.card   # playback hw card 
defaults.pcm.aec.playback_hw.rate 48000               # sample rate supported by the playback card
defaults.pcm.aec.capture_hw.card defaults.pcm.card    # capture hw card
defaults.pcm.aec.capture_hw.rate 16000                # sample rate supported by the capture card
## you may also directly set some PCM device as playback and capture device
defaults.pcm.aec.playback_pcm "playback_hw"      
defaults.pcm.aec.capture_pcm "capture_hw"             
defaults.pcm.aec.pre_loopidx 4    # loopback subdevice index for stream before aec processing
defaults.pcm.aec.post_loopidx 5   # loopback subdevice index for stream after aec processing

pcm.playback_hw {
  @args [ CARD RATE ]
  @args.CARD { 
    type string 
    default {
      @func refer
      name defaults.pcm.aec.playback_hw.card
    }
  }
  @args.RATE {
    type integer
    default {
      @func refer
      name defaults.pcm.aec.playback_hw.rate
    }
  }
  type plug
  slave.rate "unchanged"
  slave.pcm {
    type rate
    slave.rate $RATE
    slave.pcm {
      type dmix
      ipc_key 10009
      ipc_key_add_uid yes
      slave {
        pcm {@func concat strings [ "hw:" $CARD ] }
      }
    }
  }
}

pcm.capture_hw {
  @args [ CARD RATE ]
  @args.CARD { 
    type string 
    default {
      @func refer
      name defaults.pcm.aec.capture_hw.card
    }
  }
  @args.RATE {
    type integer
    default {
      @func refer
      name defaults.pcm.aec.capture_hw.rate
    }
  }
  type rate
  slave.rate $RATE
  slave.pcm {
    type dsnoop
    ipc_key 20009
    ipc_key_add_uid yes
    slave {
      pcm {@func concat strings [ "hw:" $CARD ] }
      rate $RATE
    }
    bindings.0 0
  }
}

pcm.loopback_out {
  @args [ SUBDEVICE ]
  @args.SUBDEVICE { type integer }
  type empty
  slave.pcm {
    type hw
    card "Loopback"
    device 0
    subdevice $SUBDEVICE
    channels 1
    rate 16000
    format S16_LE
  }
}

pcm.loopback_in {
  @args [ SUBDEVICE ]
  @args.SUBDEVICE { type integer }
  type empty
  slave.pcm {
    type hw
    card "Loopback"
    device 1
    subdevice $SUBDEVICE
    channels 1
    rate 16000
    format S16_LE
  }
}

# audio play to this device will be duplicated to hw (stereo) and loopback (mono)
pcm.mloopplay {
  @args [ PCM LOOPIDX ]
  @args.PCM { 
    type string 
    default {
      @func refer
      name defaults.pcm.aec.playback_pcm
    }
  }
  @args.LOOPIDX {
    type integer
    default 4 
  }
  type route
  slave.pcm {
    type multi
    slaves.a.pcm $PCM
    slaves.a.channels 2
    slaves.b.pcm {  # loopback null sink
      @func concat
      strings [ "plug:loopback_out:" $LOOPIDX ]
    }
    slaves.b.channels 1
    bindings.0 { slave a channel 0 }
    bindings.1 { slave a channel 1 }
    bindings.2 { slave b channel 0 }
  }
  slave.channels 3
  ttable.0.0 1
  ttable.1.1 1
  ttable.0.2 0.5
  ttable.1.2 0.5
}

# combine mic (ch 0) and loopback (ch 1) to single recording
pcm.mlooprec {
  @args [ PCM LOOPIDX ]
  @args.PCM { 
    type string 
    default {
      @func refer
      name defaults.pcm.aec.capture_pcm
    }
  }
  @args.LOOPIDX {
    type integer
    default 4 
  }
  type multi
  slaves.a.pcm $PCM
  slaves.a.channels 1
  slaves.b.pcm {  # loopback capturing interface
    type dsnoop   # to align with capture_hw, avoid PortAudio error
    ipc_key 10099
    slave.pcm {
      @func concat
      strings [ "loopback_in:" $LOOPIDX ]
    }
  }
  slaves.b.channels 1
  bindings.0 { slave a channel 0 }
  bindings.1 { slave b channel 0 }
}

pcm.aec_internal {
  @args [ CAPPCM PRELOOPIDX POSTLOOPIDX ]
  @args.CAPPCM { 
    type string 
    default {
      @func refer
      name defaults.pcm.aec.capture_pcm
    }
  }
  @args.PRELOOPIDX {
    type integer
    default {
      @func refer
      name defaults.pcm.aec.pre_loopidx
    }
  }
  @args.POSTLOOPIDX {
    type integer
    default {
      @func refer
      name defaults.pcm.aec.post_loopidx
    }
  }
  type asym
  capture.pcm {  # -i for aec script
    @func concat 
    strings [ "mlooprec:" $CAPPCM "," $PRELOOPIDX ]
  }  
  playback.pcm {   # -o for aec script
    @func concat
    strings [ "loopback_out:" $POSTLOOPIDX ]
  }
}

pcm.aec {
  @args [ PLYPCM PRELOOPIDX POSTLOOPIDX ]
  @args.PLYPCM { 
    type string 
    default {
      @func refer
      name defaults.pcm.aec.playback_pcm
    }
  }
  @args.PRELOOPIDX {
    type integer
    default {
      @func refer
      name defaults.pcm.aec.pre_loopidx
    }
  }
  @args.POSTLOOPIDX {
    type integer
    default {
      @func refer
      name defaults.pcm.aec.post_loopidx
    }
  }
  type asym
  playback.pcm {
    @func concat 
    strings [ "mloopplay:" $PLYPCM "," $PRELOOPIDX ]
  }   
  capture.pcm {
    @func concat
    strings [ "loopback_in:" $POSTLOOPIDX ]
  }
}