C-Media USB Audio Device (0d8c:000c) volume scale

C-Media USB Audio Device (0d8c:000c) volume scale

[Alexander Schlarb]

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Hi everybody!

I've just opened what I think is a bug at GitHub[1] and have been told to send 
it to this list instead.

System configuration:
 - http://www.alsa-project.org/db/?f=fb914e7a6b8d91993b00d61c94c885e8d2ede527
 - https://github.com/opensrc/alsa/issues/4 (some additional PulseAudio stuff)

My problem:
I have a DeLock USB audio device with an C-Media audio chip. When changing the 
volume in alsamixer there is no problem, but when changing the volume through 
any PulseAudio frontend (in my case either pavucontrol or veromix-plasmoid), 
all volumes below 30% in the GUI are shown as 0% in alsamixer and no sound is 
played.
The PulseAudio wiki[2] blames this on ALSA for exporting incorrect dB 
information. However there is a StackExchange answer[3] which suggests adding 
the parameter ignore_dB=1 in /etc/pulse/default.pa which fixed the issue, so 
I'm not sure if this is indeed ALSAs fault?

Please tell me if this can be fixed in ALSA or if this might be a PulseAudio 
bug...

With best regards,
Alexander Schlarb

[1] https://github.com/opensrc/alsa/issues/4
[2] 
http://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/User/PulseAudioStoleMyVolumes/#butthisisevilmypcmcontrolisalwayssetto100thisway
[3] http://askubuntu.com/questions/15069/how-do-i-change-the-way-ubuntu-adjusts-my-volume-mixer-levels

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Re: C-Media USB Audio Device (0d8c:000c) volume scale

[Clemens Ladisch]

Alexander Schlarb wrote:
> I have a DeLock USB audio device with an C-Media audio chip. When changing the
> volume in alsamixer there is no problem, but when changing the volume through
> any PulseAudio frontend (in my case either pavucontrol or veromix-plasmoid),
> all volumes below 30% in the GUI are shown as 0% in alsamixer and no sound is
> played.
> The PulseAudio wiki[2] blames this on ALSA for exporting incorrect dB
> information. However there is a StackExchange answer[3] which suggests adding
> the parameter ignore_dB=1 in /etc/pulse/default.pa which fixed the issue, so
> I'm not sure if this is indeed ALSAs fault?

ALSA exports the dB information that is reported by the device.

It might be possible to override this information in the driver if you
can determine what the actual mapping between raw mixer values and dB
is.


Regards,
Clemens