Comment 12 for bug 1210129

Created attachment 66151
x = alsamixer pecentage for the PCM control. y = corresponding volume in dB.

I have an ASUS P5KPL-1600 motherboard with a VIA VT1708B 8-Ch chip managed by snd-hda-intel. The volume control in pavucontrol, Gnome's sound preferences and all apps with flat-volume enabled is too non-lineal and just plain wrong.

alsamixer has two useful controls for output volume:
PCM: goes from -40.25dB in 0% through 0dB in 53% to 14dB (*with clipping*) in 100%. (This is not linear at all, see graph.png, attached.)
Master: goes from 0dB in 0% (very quiet output) to 6.75dB (without any clipping, loud and clear) in 100% with 0.25dB = 3.75% increments.

When, in PulseAudio 2.1, I set the volume in 100% it maxes out both PCM and Master, so I get a quite distorted sound. This is expected, but the scale is wrong: 100% is 0dB but it should be 14dB.

The base should be at -14dB, or 58%, when PCM is at 0dB (53%) and Master at 6.75dB (100%), but it is at -20.75dB (45%), with Master and PCM at 0dB, with very quiet output. The difference in sound pressure between 45% and 53% is very large.

Between -20.75dB (45%) and -68dB (7%) the volume does not change at all. All controls in alsamixer remain the same.

Between -68dB (7%) and -108.24dB (2%) the PCM control goes down to zero, and any less than that results in muted output.

This behaviour is quite strange and I don't know how much of it is pulseaudio's fault, how much is the alsa driver's and how much is mine.

Thanks.