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

Arun Raghavan arun at accosted.net
Thu Apr 30 02:30:30 PDT 2015

On 30 April 2015 at 14:55, Tanu Kaskinen <tanu.kaskinen at linux.intel.com> wrote:
> 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.

We do have the idea of a base volume that provide UI hints for this case.

-- Arun

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