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

[Raymond Yau]

2010/2/17 Jaroslav Kysela <perex at perex.cz>

> On Tue, 16 Feb 2010, Lennart Poettering wrote:
>
> > On Tue, 16.02.10 14:40, Mark Brown (broonie at opensource.wolfsonmicro.com)
> wrote:
> >
> >>
> >> 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...).
> >
> > I remember that a while back we had a discussion on alsa-devel
> > regarding the fact that ALSA does not define relative to what the dB
> > values reported by the mixer elements actually are measured. Some
> > mixer controls export dB values relative to max amplification (e.g. my
> > integrated USB speakers here), others relative to the output of some
> > other mixer element, and others relative to different standard or
> > not-so-standard output voltages.  And there is no API to figure out
> > what the base is.
> >
> > Now, what Jaroslav listed above suggests that he chose carefully where
> > he put 0dB. I was just wondering about that. Jaroslav, how did you
> > choose where to put 0dB?
>
> Basically, if I remember correctly the discussion, 0dB on all elements
> should main unchanged volume, <0dB attenuation and >0dB gain. We cannot
> measure precisely other components on path like analog volume wheels
> (like SB MP3+ has to change line-out volume), analog amplifiers and other
> analog signal modificators.
>
> So, if you use one headphones and speakers with defined and fixed volume
> settings, you can measure differences for the card with broken dB volume
> ranges. I just used another HDA card in notebook with 0dB settings on all
> playback controls on path, captured stream from this card on my USB card
> and played this stream back on my USB card watching and relating the
> volume levels according dB values. It's not 100% correct, but at least
> it's something to start with.
>
>                                        Jaroslav
>
>  <http://mailman.alsa-project.org/mailman/listinfo/alsa-devel>
>

Yes, 0dB for 10 bands graphic equalizer of au8830 should be no gain and no
attenuation

how can I calibrate the au8830 10 bands equalizer control as there are 10
bands peak values ?