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

Tanu Kaskinen tanu.kaskinen at linux.intel.com
Thu Apr 30 02:25:24 PDT 2015

On Wed, 2015-04-29 at 21:12 +0200, Wilck, Martin wrote:
> On Mi, 2015-04-29 at 19:17 +0300, Tanu Kaskinen wrote:
> > > The graphical volume controls don't reflect this; thus user control
> > > input volume is almost impossible at higher levels than 25%. Volume will
> > > appear to change non-predictably to users.
> > 
> > PulseAudio compensates coarse hardware volume by applying software
> > volume when necessary. This means that users get a smooth volume curve.
> > For example, you presented a nice table of different volume levels, and
> > there was this line:
> > 
> > PA(%)   PA(dB)  Captu   Boost   Capture+Boost-66dB
> > 56%     -15.00  30.00   12.00   -24.000000
> > 
> > The ideal situation would be where the second and the last column would
> > be equal, but in this case there's a 9dB difference. But no worries,
> > PulseAudio compensates that by amplifying the signal by 9dB in software.
> OK, I didn't know that. Thank you. I still think that Pulseaudio should
> rather apply the hardware volume control in "coarse first, fine later"
> order, eliminating the need for software volume compensation (which
> would infer distortion unless I am mistaken).

Yes, software amplification will in general cause a more noise than
doing the same amplification in hardware (assuming an analog amplifier),
but as you pointed out yourself earlier, we can't just switch the
Capture and Boost control order, since on some hardware the Boost
amplifier is very noisy. You're probably right that the Boost control
should be separate from the normal volume slider, but we don't currently
have a mechanism to expose the Boost control in UIs.


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