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

[Sean Greenslade]

On Wed, Jul 13, 2022 at 05:39:25PM -0400, Richard Cooke wrote:
> Holy cow I may have fixed it!
> 
> Rather, figured out the problem.
> 
> Further to that post I read about Skype rejecting the QU digital signal without boosting. I could see the peak VU in Audacity is much lower than I see on the mixer screen.
> 
> So in OBS I applied a 24db gain to the ch1 and CH2.  I also have OBS set to play to my virtual null-sink. And monitor the sink. In Zoom I select the null sink’s monitor as the mic and BOOM I have sound!
> 
> Oh wow!  I have to vacate the venue now. I will try this setup again.
> 
> If it works twice…..

I had a look at the manual for the mixer you're using, and it has the
ability to change what is routed to each of the 32 USB channels. That's
probably a much simpler way of getting the signals that you want to
always be in channels 1 and 2. No pulse / ALSA / JACK tweaking
necessary.

I would suggest changing channels 1 and 2 to be LR mix pre-fader. If your
incoming signals are mixed at an appropriate level, that should get you
what you need. If they're still too low, you might want to use a group
or matrix in post-fader mode to create a boosted copy of the main mix.

You could even apply a compressor to the matrix/group with a fairly
heavy ratio and makeup gain but a slow release. That would help tamp
down the dynamic range for the stream if your performances have
widely-varying loudness.

--Sean