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

Raymond Yau superquad.vortex2 at gmail.com
Wed Apr 22 19:53:25 PDT 2015

> Hello,
> there has been some discussion about Mic Boost  / Dock Mic Boost in the
> past already. Some have reported no Mic output at all without Boost,
> other say that enabling Boost will cause high noise on their systems.
> I have another point here that AFAICS hasn't been reported yet.
> It has been caused by the commit e6051cdf "alsa-mixer: Prefer moving
> "Capture" before moving boosts"
> (
> (see also
> https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/1085402).
> In short, on my system, input volume control is hardly possible above
> 25% because of this patch.

> The effect that I am seeing is as follows: I have two merged volume
> controls for my Mic, "Capture" and "Dock Mic Boost".

It strange that you just have two instead of three if you have dock mic

If the internal mic has no boost control, the dB range is suddenly
increased when you plug Mic or Dock Mic  ?

Since alc282 has a separate dmic  , this mean the driver need to use
dynamic ADC switching if your laptop internal Mic use dmic instead of
switching input sources with the audio mixer as selector

They are applied by
> PA in the order encountered in the path conf file. On my system (Fujitsu
> Lifebook E744 with Realtek ALC282 Codec), the "Capture" Amp has a range
> of -18..30 dB in 0.75 dB steps, and "Dock Mic Boost" has 4 12dB steps
> (0, 12, 24, 36). PA merges these two controls to a single volume control
> with an overall range of -18..66dB. Normalizing at the max, PA converts
> this to -84..0dB, where the Boost comes in at -36dB, or 25% of the
> scale. The "base volume", calculated from the "offset" of the ALSA amp,
> is at -66dB or 8%.

> Because of the above patch, the "Capture" control is used first. Thus
> the range from -84...-36 dB (or 0..25%, because of the non-linearity of
> PA's volume control) is covered with "Capture". Above that level,
> "Capture" is always held at 100% and only "Doc Mic Boost" changes. This
> means that above 25%, there are only 3 steps that are actually possible:
> -24dB / 40%, -12dB / 63%, and 0dB / 100%.
> => There is no "smooth" volume control above 25%.
> The graphical volume controls don't reflect this;

alsamixer -c0 cannot reflect the change on pulseaudio software volume ?

Do this occur only in dock Mic?

You need to check whether the driver set the amp in of the correct audio
input correctly when using dock mic

Do pactl list source  indicate the dock Mic is active port ?

thus user control
> input volume is almost impossible at higher levels than 25%. Volume will
> appear to change non-predictably to users.
> By changing the ordering of "Capture" and "Mic Boost" in the path conf
> file /usr/share/pulseaudio/alsa-mixer/paths/analog-input-dock-mic.conf,
> I can get smooth changes over the whole dynamic range again. Therefore I
> reckon that commit e6051cdf should be reverted because the effect
> described here is general, while the noise level seems to be different
> between models: On my system, there is no perceivable difference in
> noise level if the overall volume is the same (thus, 30dB "Capture" +
> 0dB "Boost" has the same noise level as 18 dB "Capture" and 12 dB
> "Boost" or -6dB "Capure" and 36dB "Boost").
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