[pulseaudio-discuss] LADSPA Per Channel\Audio Woes

Tanu Kaskinen tanuk at iki.fi
Fri Oct 14 14:44:16 UTC 2016

On Thu, 2016-10-13 at 09:57 -0400, Dylan Taft wrote:
> Thanks for your reply!
> load-module module-alsa-sink device=upmix20
> Hmm, when I put that in my default.pa, and set the profile to off for
> my card - and restart pulse, speaker-test hangs.  Other apps will just
> not play sound.  After closing everything and reopening, it seems to
> work.
> Maybe I should reboot - other apps could be grabbing the soundcard
> before pulse gets it?

In your .asoundrc you have this:

pcm.!default "upmix20"

That makes upmix20 the default device for all alsa applications.
Pulseaudio should be the only application that uses upmix20, so you
should not set pcm.!default. The stock configuration of Ubuntu will set
pulseaudio as the default device for alsa applications, and that's the
way things should be.

> I would NOT want to use dmix underneath pulse, right?  Would probably
> add a lot of latency.

Yes, using dmix under pulseaudio is generally a bad idea.

> Is it possible or a _good_ idea to move the LADSPA configuration to
> run directly in Pulse instead of Alsa?
> https://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/User/Recipes/ActiveSpeakerCrossoverLADSPA/
> There is one example of that, but it's a bit hard to understand.  Are
> you aware of any better documentation?  Looks like you split the main
> channel into 4 mono channels, apply the ladspa filter to each, then
> recombine. Is that the most sane way to do this?

I believe it's the only possible way at the moment. Doesn't seem very
sane, but if it works, that's great. Doing the filtering in alsa seems
saner to me. In principle I'm not against doing filtering in
pulseaudio, however. It would be nice if someone could implement per-
channel configuration support in module-ladspa-sink.


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