[pulseaudio-discuss] Mic Boost on AC97 audio causes bad behavior of mic volume control

[Raymond Yau]

> I did observe something by ear, but it's a long story. Since you asked
> for it, the full story is related to
> http://lists.nongnu.org/archive/html/qemu-devel/2015-04/msg02271.html,
> and goes like this:
>
> I (have to) run Microsoft Lync for telephone conferencing in a Windows
> guest on Qemu/KVM under Linux. I use Qemu's spice audio protocol to link
> my sound sources/sinks to the Windows guest. The Windows guest sees an
> emulated Intel HD Audio codec (ICH6 or ICH9) that has a 74dB volume
> scale for capture. For unknown reasons, Windows uses only the upper
> ~30dB. Therfore setting the Windows volume slider to 1% lets the "HW"
> volume in the emulated HD audio chip jump ~40% immediately. See the
> above qemu-devel post for details.
>
> The libvirt spice server communicates this percentage  to PA. PA is
> using the "48dB Capture + 36dB Boost" = 84dB volume scale. Setting this
> to 40% results in Capture=+30dB (maximum) and Boost=+12dB. Again, this
> happens if I set just 1% volume under Windows, about the lowest possible
> setting!
>


 are you using pulseaudio as backend ?

http://git.qemu.org/?p=qemu.git;a=commitdiff;h=6e7a7f3d9bc2031b4c93c05400b18775ba1b1f55;hp=a394aed235d6b3f048eeae83289f4d21eca7023c

qemu seem using stream volume control
pa_context_set_source_volume_by_index() instead of source volume control
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