[alsa-devel] Verifying mixer dB data/Invalid dB data from USB cards, especially Aureon 5.1 MkII

Lennart Poettering mznyfn at 0pointer.de
Tue Feb 16 15:26:34 CET 2010

On Tue, 16.02.10 09:08, Clemens Ladisch (clemens at ladisch.de) wrote:

> Lennart Poettering wrote:
> > Getting back to the invalid dB data from the USB cards: the question
> > is whether the USB descriptor data is badly parsed, and the dB
> > mismatch hence systematic for USB cards,
> USB descriptors use units of 1/256th dB, while ALSA uses 1/100th dB.
> When the level is computed from the minimum plus a multiple of the step
> size, rounding errors add up considerately.
> ALSA 1.0.21 (kernel 2.6.32) added a different TLV type that reports the
> range with the min/max values to minimize those rounding errors.

I am really sure that the discrepancy I measure with the Aureon is way
beyond rounding errors.


Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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