USB Sound Card with Multiple In/Out

I have setup Balena Sound and am using a cheap USB sound card from StarTech:

I know the USB audio input is experimental but it is working for me with the SOUND_ENABLE_SOUNDCARD_INPUT variable. The catch is it is taking the input from the MIC jacks, whereas I want to use the Line IN jack.

Is there some way to control which input from the Startech card is active?

I am using Raspberry Pi 4.

My goal is to connect this to my TV and use the TV as my master sound system for multi-room audio.


I made some progress here. From Balena Dashboard I selected my Pi 4 and opened a terminal window in the Audio container. I typed ‘alsamixer’ at the terminal and was able to change the capture device here. I actually set it to the optical input and it is working great.

However, this setting did not stick when the device was rebooted. There must be a configuration file I need to edit but cannot find it.

Maybe look at this
You could run this once in the container and then grab generated /etc/asound.state and add it to your docker image