[pulseaudio-discuss] Left/right volume unlinked in hardware?

[Colin Guthrie]

'Twas brillig, and Marti Raudsepp at 25/04/10 21:37 did gyre and gimble:
> When I adjust the volume in PulseAudio, I noticed that the volume for
> my left speaker is being reduced more than the volume of my right
> speaker. The difference is small, but annoying enough when using
> headphones.
> 
> So I set out to investigate with alsamixer and found that PA always
> prefers scaling the "Front" volume control. When I set this control to
> 100%, everything sounds fine, but reducing it does indeed introduce
> the difference I mentioned above, even if the volumes are linked in
> alsamixer.
> 
> Other volume controls such as "Master Front", "PCM" etc seem to be unaffected.
> 
> So as a workaround, I start up mplayer, pause it and set it to 100%
> volume in PA, which forces software gain control.
> 
> I don't think this is an ALSA problem? ALSA just simply interfaces all
> those volume controls to the user and can't help if some of them are
> broken.
> 
> Since PulseAudio takes control of setting the levels, I think it's
> also PA's responsibilty to also know about such hardware quirks?

Nah, it's alsa's jobs to implement quirks. No point fixing it in all
applications using alsa directly (while a rather advanced one, PA is
just an alsa client too), better to fix it where the problem lies.

> I assume that I'm not the first person to find a problem with a hw
> mixer control, but I couldn't find any such "quirk databases" in
> PulseAudio source tree.

You can create a custom mixer path that avoids using "Front" but really
this should work correctly in the first place.

Look in /usr/share/pulseaudio/alsa-mixer/

In your case somethign like:

sed -i 's/\[Element Front\]/\[Element Master Front\]/g'
/usr/share/pulseaudio/alsa-mixer/paths/*

would likely fix the problem (e.g. stop it playing with "Front" at all).

But that is probably not the most elegant of solutions and like I say
it's something that should really be solved in alsa to make the control
work correctly.

Col


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Colin Guthrie
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http://colin.guthr.ie/

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