ALSA: combining type "Dsnoop" with type "fifo"

Question

I am trying to get my Linux audio system to handle audio via ALSA. These are the requirements

1. Handle echo cancellation - I am using https://github.com/voice-engine/ec, following the steps mentioned and it works independently without a problem
2. Divide the echo canceled stream to 2
3. One going into a noise-canceling plugin again works independently, the audio output of this is used by a different program
4. The other to a compressor, the audio output of this will be the default device

Problem

I am facing problems in using "dsnoop" to share/divide the audio stream into two. When dsnoop plugins' slave is set to be a FIFO it throws an error.

executed:

sudo arecord -D default -f cd defRecording.wav -c 1 -r 32000

error:

ALSA lib pcm_direct.c:1809:(_snd_pcm_direct_get_slave_ipc_offset) Invalid type 'fifo' for slave PCM

arecord: main:828: audio open error: Invalid argument

This is the current asound.conf settings

asound.conf

pcm.!default {
    type asym
    playback.pcm "playback"
    capture.pcm "capture"
}

pcm.playback {
    type plug
    slave.pcm "eci"
}

# Stream Output 1: Final
pcm.capture {
    type plug
    slave.pcm "compressor"
}

# Stream Output 2: Final
pcm.capture2 {
    type plug
    slave.pcm "werman"
}

# Stream output 2: Noise Cancellation
pcm.werman {
    type ladspa
    slave.pcm "array";
    path "/usr/lib/ladspa";
    plugins [{
        label noise_suppressor_mono
        input {
            # VAD Threshold %
            controls [ 1  ]
        }
    }]
}

# Stream output 1: Compressor
pcm.compressor {
    type ladspa
    slave.pcm "array";
    path "/usr/lib/ladspa";
    plugins [{
        label dysonCompress
        input {
            #peak limit, release time, fast ratio, ratio
            controls [0 1 0.5 0.99]
        }
    }]
}

# Used to share the record device
pcm.array {
    type dsnoop
    slave {
        pcm "eco"
        channels 1
    }
    ipc_key 666666
}

# Writes audio coming from any sort of player to ec.input, this is read by the echo
# cancellation software.
pcm.eci {
    type plug
    slave {
        format S16_LE
        rate 32000
        channels 1
        pcm {
            type file
            slave.pcm null
            file "/tmp/ec.input"
            format "raw"
        }
    }
}

# Read FIFO output which contains echo cancelled audio
pcm.eco {
    type plug
    slave.pcm {
        type fifo
        infile "/tmp/ec.output"
        rate 32000
        format S16_LE
        channels 1
    }
    #ipc_key 666666
}

Note: eco is used to read the FIFO file which contains the echo canceled audio coming in from cancellation software. This software's input is hw:0 and records audio directly from the microphone, and then processes and passes this over to ec.output

Dsnoop works well when the slave.pcm is a hardware device but as soon as I point to something else it fails. Is there a workaround or any other solution to tackle this problem?

Answer 1

Dsnoop can only have a hardware slave so it can not take in a FIFO plugin as an input. To solve this, I made the echo cancellation software output data into 2 different FIFO files and then read that via ALSA.