[asterisk-users] Automatic Gain Control

[Brent Davidson]

Danny Nicholas wrote:
> If you are using a large number of DAHDI channels, you could designate a
> chunk of them as "non-local" since you can control RXGAIN on each channel.
> You would have to work out something with your TELCO since your'e a dead
> duck control-wise once you answer the call.
>   


Yuck.  I could see that being a temporary workaround, but it is not a 
good permanent solution.  And even as a workaround it wouldn't work for 
my application.  Each of our remote offices normally only has 1 employee 
(2 at most) and 2 incoming lines in a rollover setup.

I know I've probably asked this before but which parameters do txgain 
and rx gain control?  I've heard conflicting explanations.  Looking at 
it from a telco equipment standpoint I would say rxgain should be the 
gain on the sound received from the far end of the PSTN and txgain is 
the sound leaving the TDM card over the PSTN.  But I've seen a couple of 
explanations say that rxgain sets the volume of sound flowing into the 
zap/dahdi module from other channels and that txgain sets the volume 
flowing out of the zap module to other modules.  That would have the 
effect of reversing what seems like logical functions and make rxgain 
actually control the volume being sent out to the PSTN and txgain set 
the volume coming in from the PSTN.  I have not had opportunity to run 
any tests to verify for myself which explanation is correct.