[pulseaudio-discuss] [PATCH] alsa-mixer: Take channel mask of volume element into account when finding a subset path

[Tanu Kaskinen]

On Fri, 2011-12-30 at 16:01 +0000, Dave Williams wrote:
> > 
> > Actually, if my reasoning above makes sense, there's no need to
> > implement anything. Just remove the lfe-on-mono path from the mappings
> > in profile-sets/default.conf that don't have lfe in their channel map.
> > 
> > Can someone say why lfe-on-mono would be needed on mappings without
> > separate lfe channel?
> > 
> 
> 
> I have an example of just such a case: A Dell Inspiron 9300. There is no
> lfe PCM channel, but there is a 'Master Mono' control that controls the
> subwoofer level (I guess the separation is done in the analogue domain
> after the DACs).
> 
> For this computer, the 'Master' level control and 'Master Mono' level
> control need to be set to (approximately) the same level to get
> reasonable sound out of it.

Thanks for reporting this. Now I see the point of the lfe-on-mono path.

> At present I'm having to take volume control out of the hands of
> pulse, as I can't persuade it to do this (I've been playing with the
> analog-output-lfe-on-mono.conf path that ships with debian to no avail).
> What appears to be happening is the volume chain constructed by pulse
> looks like:
> PCM -- Master Mono -- Master
> 
> when it should be more like:
> PCM -- Master
>     \- Master Mono
> 
> The upshot being that the sub gets cranked up to max before the main
> speaker levels even start to rise when controlling volume through pulse.
> 
> There is a lot of talk on forums (e.g. ubuntu launchpad) about this
> being an ALSA issue. It isn't - ALSA is reporting perfectly reasonable
> dB levels. Pulse is just making a mess of working out the audio path.

Sounds like a Pulseaudio bug then. I won't investigate this now, so I
filed a bug: https://bugs.freedesktop.org/show_bug.cgi?id=45331

-- 
Tanu