[alsa-devel] wrong decibel data?

Lennart Poettering mznyfn at 0pointer.de
Mon Jun 14 20:41:07 CEST 2010

On Mon, 14.06.10 09:56, James Courtier-Dutton (james.dutton at gmail.com) wrote:

> On 14 June 2010 09:33, Colin Guthrie <gmane at colin.guthr.ie> wrote:
> > 'Twas brillig, and Raymond Yau at 14/06/10 01:25 did gyre and gimble:
> >> if your sound card have ac97 codec ., you can use audacity to record the
> >> output from hw:0,0 and you will see clipping occur when you set "PCM" volume
> >> above 0dB
> >
> > So the standard response is "don't do that then" :)
> >
> > That's why the base volume is shown to the user via GUIs so that they
> > can gauge the best point on the slider to use. Currently there is no
> > indication with alsa sliders at which point the 0dB "sweet spot" lies.
> >
> What do you mean.
> If you use "alsamixer", dB values are shown so it is easy to find the
> 0dB "sweet spot".

Whether dB is shown or not has nothing to do with PA. Some UIs show it,
others don't. And most UIs do show the "base volume" too, which refers
to the ALSA 0dB "comfort" point. There is nothing lost here. We just
simplified things a littl and made the volume range infinite, as well as
we unified what things look like on various hardware.

> I think it is pulse audio that hides this information when it combines
> two alsa mixer controls into one pulseaudio control.

No, we don't. The final "base volume" will be put where all sliders that
are merged are at 0dB.


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

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