[alsa-devel] wrong decibel data?

Lennart Poettering mznyfn at 0pointer.de
Mon Jun 14 20:49:22 CEST 2010

On Mon, 14.06.10 11:22, Colin Guthrie (gmane at colin.guthr.ie) wrote:

> 'Twas brillig, and James Courtier-Dutton at 14/06/10 09:56 did gyre and
> gimble:
> > 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".
> > I think it is pulse audio that hides this information when it combines
> > two alsa mixer controls into one pulseaudio control.
> But it doesn't hide it. It's shown very clearly in the volume control
> GUIs as the Base Volume.

Let me also stress that "dB" is not at all understandable to most
people. It is a very technical unit, and showing 0dB in the UI just like
that won't be very helpful for most people.

That's why we thought about this, and are recommending a color coded
slider to be exposed in the UI which encodes the range information in a
sane way that is intuitively understandable by users. In green, in
yellow and in red. (meaning hw attenuated, hw amplified, sw amplified



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

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