Enable app volume control with ALSA softvol on USB audio interface

[ulexxander]

Sharing my solution, did not find anything appropriate for me in issues here.

I am using tidal-connect-docker image on plain Raspberry Pi OS without any desktop environment, on Pi 4B model
with MOTU M2 USB audio interface that outputs to speakers.

As playback device I was setting M2: USB Audio (hw:2,0).
Because of that volume control didn't work as that device did not had any controls in ALSA.

To make volume control in Tidal app work I configured ALSA to enable softvol - software volume control and set that as a playback device in tidal-connect-docker.

Instead of M2 below put your card name, find it with aplay -L

File asound.conf

pcm.softvol {
    type            softvol
    slave {
        pcm         "hw:CARD=M2,DEV=0"
    }
    control {
        name        "SoftMaster"
        card        "M2" 
    }
}

pcm.!default {
    type             plug
    slave {
        pcm         "softvol"
    }
}

ctl.!default {
    type hw
    card "M2" 
}

File docker-compose.yml

version: "3.8"

services:
  tidal-connect:
    image: edgecrush3r/tidal-connect:latest
    tty: true
    network_mode: host
    devices:
      - /dev/snd
    volumes:
      - /var/run/dbus:/var/run/dbus
      - ./asound.conf:/etc/asound.conf
    environment:
      - FRIENDLY_NAME=malinka
      - MODEL_NAME=malinka
      - PLAYBACK_DEVICE=default
      - MQA_CODEC=false
      - MQA_PASSTHROUGH=false
    restart: always
    stop_grace_period: 1s

Further reading:

• https://alsa.opensrc.org/How_to_use_softvol_to_control_the_master_volume