[pulseaudio-discuss] How to map 2 channels from a 32-channel USB device to L/R?

[Richard Cooke]

This has been driving me crazy for a few weeks!  I do volunteer work 
around Town, and a local church got its hands on a really nice 
Allen-Heath QU-24 sound board.  It has a USB-B jack. I recently set up a 
Video camera with control computer for streaming services and events. 
The new sound board was to vastly improve the audio quality.

When I connect it to the church's "streaming" computer, running Ubuntu 
20.04 it is recognized as both a SOURCE and SINK device. In Audacity, I 
can select any of the 32-channels and see they are working.  We have our 
streaming mix (9) on CH17 and CH18, repeated on CH1 and CH2 for 
testing.  Again, Audacity has no problem selecting any of them.

They stream using Zoom, Zoom lists the QU-24 but when selected no 
audio.  We use OBS Studio 27.2.4 for the video (virtual camera), it also 
lists the QU-24 but no audio.

I figured out half of my solution by creating a virtual sink monitor 
that Zoom can use as a microphone:

# include the default.pa pulseaudio config file
.include /etc/pulse/default.pa

# null sink
.ifexists module-null-sink.so
load-module module-null-sink sink_name=Source
.endif

# virtual source
.ifexists module-virtual-source.so
load-module module-virtual-source source_name=VirtualMic 
master=Source.monitor
.endif


Which I learned from this post:

https://www.youtube.com/watch?v=Goeucg7A9qE

https://github.com/NapoleonWils0n/cerberus/blob/master/pulseaudio/virtual-mic.org


Which I tested with an analog mic into OBS that came out the Zoom meeting.


So, if OBS is not going to pickup the QU audio for me, is there a PACTL 
command I can use to path CH1/CH2 to my virtual sink?  Or, even better, 
CH17/CH18?


Thank you in advance!