[pulseaudio-discuss] [RFC] Source Output Volumes

Colin Guthrie gmane at colin.guthr.ie
Fri May 20 03:09:23 PDT 2011

'Twas brillig, and Maarten Bosmans at 20/05/11 10:23 did gyre and gimble:
>> > With flat volumes, adding per-stream volumes to capture streams makes sense.
> With these changes, would it still be possible to record audio without
> software gain? As it is now, I can record from a source that has its
> volume set to 100% and be confident that I'm getting the signal direct
> from the soundcard.
> Is that still the case with the default source output volume?

Yeah, that should still be the case. If you set the volume to of your
stream to 100%, even if some other stream is recording at 50%, the h/w
volume should be set to 100%

Of course this is all rather arbitrary, as on my h/w the gain is 0dB
when I set the volume to 0.... at 100% it's +22.5dB, so to say direct
from the sound card at 100% is a little strange.... it's getting +22.5dB :)

I guess the problem would come when recording two things at once. If you
set one to 100% (thus +22.5dB on my system) and one to the base volume
of the source it's attached to (thus ALSA's 0dB*), then the one that
expects to be recording at 0dB will actually get a signal that has gone
up to +22.5dB and then come back down in software to 0dB. This isn't
ideal, but then it's as non-ideal as it is currently and the use case
for recording two streams at the same time is rather minimal anyway, so
I don't think in all practicality, this is a big issue.

Of course if you don't use flat volumes and only use per-stream
recording volumes in your app, then the difference between the source
volume and the stream volume does come into play AFAIUI. But then if you
take the time to disable flat volumes, that's presumably a consequence
you can live with.


* I have one USB mic that reports it's range as +20dB to +50dB in alsa,
so the base volume for it is actually significantly below the ALSA 0
point on the kcontrol!


Colin Guthrie

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