[alsa-devel] wrong decibel data?

[Raymond Yau]

2010/6/7 Colin Guthrie <gmane at colin.guthr.ie>

> 'Twas brillig, and Raymond Yau at 06/06/10 01:12 did gyre and gimble:
> > 2010/5/28 Colin Guthrie <gmane at colin.guthr.ie>
> >
> >> 'Twas brillig, and Colin Guthrie at 27/05/10 15:43 did gyre and gimble:
> >>> PA should play nice with the softvol plugin so I don't think this is
> the
> >>> bit that is at fault.
> >>>
> >>> I strongly suspect that the reason has already been correctly
> identified
> >>> a while ago, which is that this card considers -48dB silent where as PA
> >>> assumes this level is -200dB. I believe it was Raymond who pointed out
> >>> the -48dB level in the HDA spec before on this list.
> >>>
> >>
> >
> > if  floating point 0.0 is -inf dB , and 1.0 is 0dB ,
> >
> > 0.5 is -6dB , 0.25 is -12 dB , 0.125 is -24dB and 0.0625 is -48dB
>
> This is just a pure mapping from dB->linear, but as this linear mapping
> is generally not "natural" there are several different approaches to
> presenting this to users. In PA, a cubic mapping is used on top of this
> basic conversion, to map to the percentage scale (0.0 to 1.0 if you like).
>
> So I'm not sure what point you're making by providing these numbers. Can
> you explain?
>
> > how can PA master volume control at 10~15% equivalent to HDA 's -48dB ?
>
> Not sure what you mean here, but I suspect it's the cubic mapping that
> is confusing you.
>

>> FWIW, I've got the same/similar h/w with a cutoff at 14% in PA as you
have.

According to your email , you mention than your hardware has a cutoff at 14%
in PA

the mixer application programmer  can select any kind of scaling in the
slider

do you mean 14% in pavucontrol or Master volume control of "pulse" device ?

but pavucontrol did not provide any dB value at any point