The pulseaudio configuration allows to remap partial sources of the multi-input device, however the exact channel used for different functions is guesswork. It's not entirely clear to me what values the master_channel_map
can receive, but I had success in selecting front-center
which gives me the mic input without any mixes, and hardware mute button correctly silences everything.
First, find out the device name of the multinput audio interface:
$ pacmd list-sources | grep name:
name: <alsa_output.usb-Focusrite_Vocaster_One_USB_V1AR19B2601E24-00.analog-surround-40.monitor>
name: <alsa_input.usb-Focusrite_Vocaster_One_USB_V1AR19B2601E24-00.multichannel-input>
In my case, the master name is alsa_input.usb-Focusrite_Vocaster_One_USB_V1AR19B2601E24-00.multichannel-input
Then add this line to the /etc/pulse/default.pa
at the bottom:
load-module module-remap-source source_name=vocaster-mic source_properties=device.description=Vocaster master=alsa_input.usb-Focusrite_Vocaster_One_USB_V1AR19B2601E24-00.multichannel-input remix=no channels=1 master_channel_map=front-center channel_map=mono
This adds a new input called "Vocaster" with the front-center channel of the multi-input device.
Optionally, mark this device as the default so you don't have to switch on boot time:
set-default-sink alsa_output.usb-Focusrite_Vocaster_One_USB_V1AR19B2601E24-00.analog-surround-40.monitor
set-default-source vocaster-mic
Afterward, restart or use pulseaudio -k
to kill the previous pulseaudio daemon. Note that doing this breaks audio in apps until they are restarted.