[Speex-dev] Re: [Iaxclient-devel] iaxclient & speex

Jean-Marc Valin jean-marc.valin at usherbrooke.ca
Thu May 3 19:27:52 PDT 2007

>> I don't see b) as being that important. Could help a bit, but you really
>> want to use a).
> I think you want to use both pieces of information, so you're not
> raising the level of a signal that's not speech.  It's _especially_
> important when you're doing EC, of course, because you don't want to
> raise the gain on an echo.

Keep in mind that this mainly controls the saturation point. Any time
you change the analogue gain, you should tell the AGC to decrease it's
gain by the same amount.

>> You don't want to make small +-10% adjustments. I would go for +-10 dB
>> at *least* (probably even 20 dB). Quantization noise issues at 16 bits
>> per sample aren't worth the trouble of doing smaller steps.
> The thing is, I don't know if mixer controls on most platforms give you
> any idea of by how many dB you're changing things, whether the changes
> are linear or not, etc -- the mixer controls are just a know with levels
> from 0<->1 (mac, I think), 0-100, or 0-255.  I raise/lower them by 10%
> or 20% of their full range, so with the 10% adjustments, you only have
> 10 steps.  That seemed a big enough jump in practice.

OK, I thought you mean a 10-20% difference in the gain, which is quite
small (< 1dB). Anyway, you don't want to be playing with that gain
unless either
1) You have clipping
2) The capture level is ridiculously low (e.g. 16-bit samples don't go
above 256 or something).


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