[alsa-devel] Mixer volume/decibel mapping

[Raymond Yau]

2010/5/21 James Courtier-Dutton <james.dutton at gmail.com>

> On 21 May 2010 07:35, Clemens Ladisch <clemens at ladisch.de> wrote:
> > James Courtier-Dutton wrote:
> >
> >> For the cards that do have this 32bit linear value, a simple lookup
> >> table is used in the kernel code to convert it to 256 step values.
> >
> > Which driver is this?  It should be changed to use the full range.
> >
>
> All creative and emu cards with a DSP.
> They use a lookup table in the driver.
>

seem a bug in the lookup table of alsa-lib

20log10(1/100) = -40dB , it should return -40dB  if set -40dB

https://bugtrack.alsa-project.org/alsa-bug/view.php?id=4883

snd_mixer_selem_set_playback_dB(<master element>, 0, -4000, +1) -> returns 0
snd_mixer_selem_get_playback_dB(<master element>, 0, &value) -> returns 0,
sets value to -9999999