[alsa-devel] wrong decibel data?
superquad.vortex2 at gmail.com
Tue Jun 15 01:43:48 CEST 2010
2010/6/15 Lennart Poettering <mznyfn at 0pointer.de>
> 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
> > >>> output from hw:0,0 and you will see clipping occur when you set "PCM"
> > >>> 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
Clipping may occur at recording if there is gain above hardware 0dB point ,
the region should be coloured as red ,
What is the meaning of the yellow region ?
For HDA base volume seem to be at the same point as the norm volume since
max_db of playback is 0dB
+12dB(400%) is even larger than the software gain 150% of PA
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