Headphone volume adjustment

[Daniel Drake]

On Fri, Jul 5, 2013 at 5:47 PM, James Cameron <quozl at laptop.org> wrote:
> The DAC volume control has the greatest range, all the way down to
> -96.625 dB, which coupled to our XO-1.75 hardware is effectively
> silent, but not guaranteed to be.  You can see the details of this
> control in the XO-1.75 and XO-4 source ... search for dac_vol_tlv.
>
> The speaker amplifier control has a range of 58.5 dB.  With this set
> to minimum on our XO-4 hardware it is also effectively silent but not
> guaranteed to be.

OK, thanks for the explanation. So, fixing the ALSA controls to
exploit the full volume range of the hardware would probably result in
an OK user experience on this point (minimum volume = inaudible
sound), and I think that would be more consistent with other ALSA
drivers behaviour, but might also come with other headaches.

So I can appreciate the effort taken to not change the audible range
and other behaviour, but simply set the mute bits when the minimum
volume is selected. So this patch looks fine to me. Thanks.

As a point of interest, the pulseaudio volume control on my desktop
automatically sets the mute bit on the underlying ALSA device when the
volume slider is dropped to zero. I presume that behaviour is
implemented by the pulseaudio core. It is probably done for the same
kinds of reasons (minimum volume not guaranteed to to be inaudible,
but muting does the trick).

Thanks
Daniel