[pulseaudio-discuss] channel_map problems with alsa

Pierre Ossman ossman at cendio.se
Tue Feb 13 23:57:19 PST 2007

Alex Malinovich wrote:
> Ok, so for the first time in about a year I can actually get sound out
> of all 4 speakers simultaneously. Yay! But, there's a problem.
> I'm using module-combine to combine alsa devices hw:0,0 and hw:0,1. The
> front and rear channels, respectively. Unfortunately, when I load
> module-alsa-sink for hw:0,1, if I set
> "channel_map=rear-left,rear-right", I get no sound. I can still play
> sounds to the sink, I just don't hear it. If I leave channel_map alone,
> or if I manually map it to either front-left,front-right or left,right
> everything works just fine. The problem comes in with how my combined
> output behaves.

The channel remapper is a bit stupid right now, so it won't move a two
channel (f-r, f-l) stream to b-r, b-l. That is why you're not getting
any audio with that channel map.

> If I change the rear-left or rear-right volumes for combined, nothing
> happens. If I change front-left or front-right volumes, it changes both
> of the speakers on that particular side. It's not a problem using things
> like audacious, but it could be a problem once I start using things like
> mplayer or totem to play DVD's and I suddenly get half of the audio
> coming out of twice as many speakers. :) Any suggestions on what I can
> try?

I would guess that you've made a mess of your channel map. The FAQ
contains an example of exactly this setup (#27).

Pierre Ossman            OpenSource-based Thin Client Technology
System Developer         Telephone: +46-13-21 46 00
Cendio AB                Web: http://www.cendio.com

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