[Asterisk-Dev] Dev Meeting this week.

[Stephan A. Edelman]

I don't think just software AGC is going to do it without significant
loss of "resolution". The peak amplitude that I'm seeing on the recorded
WAV files that appear in my e-mail is probably about 2-4% of maximum.
Software amplifying this will result in significant noise and distortion
because the S/N ratio is so low. (This still may be better than not
being able to hear it at all when listening to your voicemail over
PSTN).

I have no idea if the zap gain can be adjusted on the fly with the
current driver implementation, or if it requires additional ioctl's or
other fixes to make this work. 

I think tying a relatively fast acting software AGC to the hardware gain
of the zap interface would be ideal. 

Stephan. 

-----Original Message-----
From: asterisk-dev-bounces at lists.digium.com
[mailto:asterisk-dev-bounces at lists.digium.com] On Behalf Of Steve Kann
Sent: Thursday, April 21, 2005 10:40 PM
To: Asterisk Developers Mailing List
Subject: Re: [Asterisk-Dev] Dev Meeting this week.


On Apr 21, 2005, at 10:31 PM, Stephan A. Edelman wrote:

>
> I also consistently get voicemail recordings from a zap channel that 
> are barely audible. The gain on the zap channel needs to be adjusted 
> on the fly when a voicemail message is left. Perhaps, some fancy 
> software AGC and companding (to keep the volume at say, 90% of the 
> clipping level) in combination with predefined zap gain.

libspeex has a reasonably good software AGC implementation, in the
preprocessor (you don't need to use the codec for this).

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