[alsa-devel] Handling of the DXS controls in the via82xx driver

Clemens Ladisch clemens at ladisch.de
Mon Mar 29 14:56:11 CEST 2010

Soeren D. Schulze wrote:
> before my latest upgrade to Linux 2.6.32 (yes, sorry, it's Debian), I
> had four levers in my alsamixer: VIA DXS, VIA DXS 1, VIA DXS 2 and VIA
> DXS 3.  They controlled the hardware mixing when accessing the sound
> device multiple times.
> Now they have disappeared.
> As I'm not an ALSA developer, I don't realize the intended effect of
> this change,

Hiding these controls is an intended effect, because normal mixers
do not show application-specific controls that could go away or be
reset at any time.

> but the actual effect is that I cannot change the DXS volumes any
> more.

You can with the hwmixvolume tool in the alsa-tools package (version
1.0.23, not yet released).

> mplayer still controls the global PCM volume.  Well,
> in fact, there is one way.  While an mplayer is running, I can do:
> amixer cset numid=47,iface=PCM,name='PCM Playback Volume' 24,24
> When restarting mplayer, the volume is reset to 31,31 (maximum).

The old behaviour was considered buggy: these stream controls are
logically associated with a stream opened by an application, not with
a particular hardware stream.

> The bad thing about it is that 31,31 is a really bad setting for my
> poorly engineered sound card.  It distorts a lot.

If the card cannot handle any loud output, then all outputs from any
source must be restricted, so the logical place for lower volume would
be the "Master" or "PCM" controls.


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