[alsa-devel] Verifying mixer dB data/Invalid dB data from USB cards, especially Aureon 5.1 MkII
superquad.vortex2 at gmail.com
Wed Feb 17 08:37:26 CET 2010
2010/2/17 Eliot Blennerhassett <linux at audioscience.com>
> There are two separate issues here.
> 1) Incorrect dB<->linear mapping
> ALSA Volume/Gain controls returning incorrect information about mapping
> from linear values to dB. E.g. adding "6dB" to the Volume controls
> while subtracting 6dB in software does not result in 0dB overall gain.
> For volume controls the convention is 0dB == multiply by 1.0 == no
> change. Any sane digital volume control should obey this.
> For analog volumes, the 0dB position is entirely arbtrary, as I discuss
For the alsa db values are in step of 1.5 dB or 3.dB ,
but the software shift one bit is 10 log 2 = 3.0102996* dB
That 's why adding "6dB" to the Volume controls
while subtracting 6dB in software does not result in 0dB overall gain.
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