[alsa-devel] wrong decibel data?

Raymond Yau superquad.vortex2 at gmail.com
Fri Apr 9 15:49:06 CEST 2010

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?

The DR of 16bit audio is 96dB


The 16-bit compact disc <http://en.wikipedia.org/wiki/Compact_disc> has a
theoretical dynamic range of about 96
about 98 dB for sinusoidal signals, per the formula
[6] <http://en.wikipedia.org/wiki/Dynamic_range#cite_note-seeber-5>).
Digital audio with 20-bit digitization is theoretically capable of 120 dB
dynamic range; similarly, 24-bit digital audio calculates to 144 dB dynamic
digital audio recording and playback chains include input and output
converters and associated analog circuitry, significantly limiting practical
dynamic range. Observed 16-bit digital audio dynamic range is about 90 dB

The SNR of your codec is 95dB SNR

This mean that PA not using all the sum of the volume of the amplifer and
volume knob widget to calculate the dB value of your codec

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