[alsa-devel] wrong decibel data?

[Raymond Yau]

2010/4/9 Nicolo' Chieffo <nicolo.chieffo at gmail.com>

> On Fri, Apr 9, 2010 at 1:11 AM, Raymond Yau <superquad.vortex2 at gmail.com>
> wrote:
> > Mute Capable (1 bit) reports if the respective amplifier is capable of
> > muting. Muting implies a –infinity gain (no sound passes), but the actual
> > performance is determined by the hardware.
> >
> > http://thread.gmane.org/gmane.linux.alsa.devel/39262/focus=16100
>
> I think you missed the point, I'll explain again.
> I'm not complaining that at 0% the audio is not mute, as the bug you
> linked.
>
> >>> Clemens Ladisch (developer) 2004-11-09 09:26
> >>>    The AD1981B's datasheet says that the maximum attenuation is 46.5 dB
> >>> (which conforms to the AC'97 specification).
> >>> To mute, use Mute.
>
> In fact my problem is that at 0% I get mute, but I shouldn't (as
> reported by that developer), since the max attenuation is not -inf,
> but -48 dB.
> So if you prefer, you could see this issue from a different point of
> view: at -48 dB the audio should be still audible, but it's not.
>
> so you have to decide where the issue resides (but definitely not in
> pulseaudio)
> a) it is ok that the audio is mute at 0% (in this case you have to
> declare -inf dB)
> b) the audio level is really -48 dB (in this case the volume shouldn't
> be cut off completely, but simply quite low)
> Which one do you prefer?
>

if you had read studied the bug report

"On my Compaq R3070 laptop setting Master and Master Mono controls to 0 does
not result in no sound out. I still get audio at a low level."

The user only set Master and Master mono controls to 0.

http://www.analog.com/en/audiovideo-products/audio-codecs/ad1981b/products/product.html

Refer to Figure 1 THe functional BLock Diagram , you should notice that
there is another volume control in the audio path from DAC to LINE_OUT

The Master Volume and Master mono control have dB range from -46.5dB to 0dB

But the PCM Out volume control has dB range of -34.5dB to +12 dB

That is you have to sum the atten of the hardware volume controls in the
audio path