[alsa-devel] wrong decibel data?

[Raymond Yau]

2010/6/14 James Courtier-Dutton <james.dutton at gmail.com>

> On 14 June 2010 10:54, Raymond Yau <superquad.vortex2 at gmail.com> wrote:
> > 2010/6/14 James Courtier-Dutton <james.dutton at gmail.com>
> >> 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.
> >>
> >
> >
> > The base volume seem to be the software 0dB point , (no software
> > gain/atten), but the user want the hardware 0dB point (no hardware
> > gain/atten if the hardware can provide hardware gain
> >
> > This hardware 0dB point is extremely important when you want to record
> using
> > line in and line out
>
> alsamixer gives the hardware 0dB point.
>

you are right ,

For ac97 Base volume is the real hardware  0dB point of PCM volume, and
Volume NORM is just the max_dB of +12dB which PA labeled it as 100% aka 0dB
aka Volume NORM

For HDA , there is no yellow region because max_dB is 0dB , Base Volume and
NORM is at the same point

http://en.wikipedia.org/wiki/Line_level

How can I get distortion free recording by line in of ac97 sound connected
to line out of HDA onborad and vice versa ?

http://pulseaudio.org/wiki/WritingVolumeControlUIs#Colouredvolumesliders