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.