Speex dev - Jun 2007 - Noise suppression less than AGC gain

>> Yes, after I stop speaking, the noise slowly starts climbing again, and
>> if I peek at st->agc_gain, that's slowly climbing too. I think
part of
>> the trouble is that the noise in here isn't uniform white noise;
there's
>> traffic outside the window and people walking in the hallway outside my
>> door. Each little event is enough to cause the AGC to increase a little
>> bit.
> 
> Hmm, I guess it's sort of the expected behaviour. It's pretty hard
for
> the AGC to know whether these "events" are desirable or not and
whether
> it should adapt to them.
Aye. I have some silent hope that some day a perfect VAD will arrive, 
and then that could be used to adapt the AGC :)
>> Alternately, perhaps it could be made so that noise suppression scales
>> with agc_gain? (IE, if you're multiplying by 10 for the gain,
multiply
>> noise reduction by 10 as well).
> 
> Well, you can always force the values yourself. Look for
> SPEEX_PREPROCESS_SET_NOISE_SUPPRESS
> and
> SPEEX_PREPROCESS_SET_AGC_MAX_GAIN
> Both are in dB (integer)
I did that (set noise suppress to -30 and the max gain to 15), and that 
fixes the problem for me. But as this seems to be a fairly common 
environment, I thought perhaps it would make sense to tune the defaults 
slightly.

>> Hmm, I guess it's sort of the expected behaviour. It's pretty
hard for
>> the AGC to know whether these "events" are desirable or not
and whether
>> it should adapt to them.
> 
> Aye. I have some silent hope that some day a perfect VAD will arrive,
> and then that could be used to adapt the AGC :)
OK, I'll wait for your patch then ;-)
> I did that (set noise suppress to -30 and the max gain to 15), and that
> fixes the problem for me. But as this seems to be a fairly common
> environment, I thought perhaps it would make sense to tune the defaults
> slightly.
Well, I can change the defaults and then people with different setups
(e.g. no noise and low input volume) will ask me to change it the other
way... In the end, the only fix is to improve the AGC adaptation
decision, including (but not only) the VAD.

	Jean-Marc

Jean-Marc Valin escreveu:
> 
> Well, I can change the defaults and then people with different setups
> (e.g. no noise and low input volume) will ask me to change it the other
> way... In the end, the only fix is to improve the AGC adaptation
> decision, including (but not only) the VAD.
Could that be a run time variable? So it could be adjusted somehow by a 
user interface, for extreme situations.

Alain