[alsa-devel] Softvol controls

[Takashi Iwai]

At Tue, 20 Nov 2007 01:51:51 +0100,
Lennart Poettering wrote:
> 
> 3) Some newer soundcards lack a hw volume control if I understood
>    correctly. Unfortunately I don't have access to them myself. But
>    apparently if PulseAudio is run on those devices, volume control in
>    PulseAudio doesn't work at all. Apparently ALSA uses softvol to add
>    a software volume control (attenuation) to the mixer on those
>    soundcards. PA finds that control and makes use of it -- however,
>    since it accesses the PCM via the raw devices (hw:, surround41: and
>    so on) softvol doesn't work: i.e. the volume that people can change
>    through the PA mixer is not reflected in any way in the audio
>    output.
> 
>    Now, is there a way I can detect for a mixer element if it is
>    "real" or if it is implemented only for the "plughw" PCM? As it
>    seems the "hw:0" mixer device does contain "virtual" tracks, isn't that a
>    bit strange? Shouldn't the virtual mixer tracks be available only
>    in a mixer device "plughw:0"? That at least would be symmetric to
>    the PCM case, wouldn't it?

Check snd_ctl_elem_info_is_user().  All softvol controls are
implemented as user elements.


Takashi