[alsa-devel] Verifying mixer dB data/Invalid dB data from USB cards, especially Aureon 5.1 MkII

[Raymond Yau]

2010/2/24 Clemens Ladisch <clemens at ladisch.de>

> Lennart Poettering wrote:
> > On Tue, 23.02.10 11:08, Clemens Ladisch (clemens at ladisch.de) wrote:
> > > Lennart Poettering wrote:
> > > > Unfortunately there is no way from the simple mixer to the lower
> level
> > > > mixer.
> > >
> > > From the check_unplugged function in
> alsa-utils/alsamixer/mixer_widget.c:
> > >
> > >     err = snd_mixer_get_hctl(mixer, mixer_device_name, &hctl);
> > >     if (err >= 0)
> > >             ctl = snd_hctl_ctl(hctl);
> >
> > But that still doesn't give me a hint which snd_ctl_eleme_t belongs to
> > which snd_mixer_eleme_t, does it?
>
> Not really; the point of the simple mixer interface is to abstract away
> some of the ctl naming conventions.
>
> > > > It would be great if the smixer would include some API that gives me
> a
> > > > hint to which device/subdevice a specific snd_mixer_elem_t belongs
> to.
> > >
> > > Often, there is no 1:1 correspondence between mixer elements and PCM
> > > devices.  Only mixer controls with interface PCM (not MIXER) have
> (sub-)
> > > device numbers, and at the moment this is used only for controls that
> > > are associated with the streams of hardware-mixing-capable cards.
> >
> > Which are not that many, right? Not HDA at least?
>
> No, most recent hardware was designed for software mixing.  Only the
> snd-emu10k1, snd-via82xx and snd-ymfpci drivers implement such controls.
>
>
> Regards,
> Clemens
>
>
However the playback subdevices of some HDA codec did not support the same
range of channels

(e.g. vt1708s has two playback subdevices ,

 if independent HP mode is ON , one subdevice can only suppport 2 channels
and the other subdevices support 2 ,4 ,6

if independent HP mode is OFF , the subdevice may support 2, 4, 6 and 8
channels