[pulseaudio-tickets] [Bug 54096] New: Problems with volume control in VIA VT1708B 8-Ch

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=54096

             Bug #: 54096
           Summary: Problems with volume control in VIA VT1708B 8-Ch
    Classification: Unclassified
           Product: PulseAudio
           Version: unspecified
          Platform: x86-64 (AMD64)
        OS/Version: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: alsa
        AssignedTo: pulseaudio-bugs at lists.freedesktop.org
        ReportedBy: agustin at dallalba.com.ar
         QAContact: pulseaudio-bugs at lists.freedesktop.org
                CC: lennart at poettering.net


Created attachment 66151
  --> https://bugs.freedesktop.org/attachment.cgi?id=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.

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