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

[Raymond Yau]

>

> >
http://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/Developer/Clients/WritingVolumeControlUIs/
>
> As I already wrote, the way it is today, if I set 100%/0dB either with
> the GNOME volume control, "alsamixer -D pulse", or "pactl
> set-source-volume 2 100%", the result is 30dB Capture + 24dB Boost,
> which is *not* maximum level. So the user is currently not correctly
> informed about the "real 0dB", even if you factor in the boost.

http://freedesktop.org/software/pulseaudio/doxygen/volume.html

pulseaudio documentation/wiki on volume only mention sink

>
>
> However, for line in, the jumpy behavior of the current input control
> would be even worse than for the Mic. My guess would be that for line
> in, Boost had better be set to 0dB all the time, and "real 0dB" would be
> "30dB Capture + 0dB Boost". You just gave another argument for not
> merging "Mic Boost" into the overall volume.


How did you add Line in support ?

1) use hint add_jack_modes = 1

2) retask mic in jack to line in jack by early patching

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/tree/Documentation/sound/alsa/HD-Audio.txt

- add_jack_modes (bool): add "xxx Jack Mode" enum controls to each
  I/O jack for allowing to change the headphone amp and mic bias VREF
  capabilities

- line_in_auto_switch (bool): enable/disable the line-in auto-switch
  feature; default false

For line in recording, user expect pavucontrol provide a point at the
volume slider which set  Capture Volume and Line Boost at 0dB and no
pulseaudio software volume similar to spdif passthrough to prevent clipping
occur

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/log/sound/pci/hda?qt=grep&q=mic+boost

HDA driver have quirks about limiting the internal mic boost,

The base volume of pulseaudio source is not constant any more

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/commit/sound/pci/hda?id=3e0d611b2045b230c3acfb05c3b5ce53b09f6cdd
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