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

[Raymond Yau]

2010/2/16 Mark Brown <broonie at opensource.wolfsonmicro.com>

> On Tue, Feb 16, 2010 at 03:32:01PM +0100, Lennart Poettering wrote:
> > On Tue, 16.02.10 09:24, Jaroslav Kysela (perex at perex.cz) wrote:
>
> > > Line: 0dB..47.81dB          # seems correct -47.81dB..0dB
> > > Line Capture: -0.18dB..23.81dB      # seems correct
> > > -17.81dB..6.18dB
>
> > Hmm, how did you choose where to put 0dB?
>
> The Line one looks like someone got attenuation and gain confused, which
> is a fairly common mistake for people to make when copying information
> from one place to another.  Possibly a similar thing going on with the
> Line Capture control, plus a fixed 6dB gain (which may well be a
> separate amp...).
>

Correct me if I am wrong

0dB point is needed when you recording from line-in by connected loopback
cable to line out.

The captured signal is supposed to be the same as the playback signal when
you set both playback volume and capture volume to 0dB ,

if you set playback volume over 0dB , clipping occur in the captured signal
,

if the playback volume is less than 0dB , captured signal will be less than
the playback signal.