[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?
>

http://en.wikipedia.org/wiki/Decibel

In electronics, the decibel is often used to express power or amplitude
ratios (gains), in preference to arithmetic ratios or percentages. One
advantage is that the total decibel gain of a series of components (such as
amplifers and attenuators) can be calculated simply by summing the decibel
gains of the individual components.