[asterisk-users] Clarifying RX and TX gains

[cb]

I've done gain tuning as per the info I've found online. I've got my  
RXGain set so my volumes list as about 14,800 (using a milliwatt test  
number and ztmonitor -vv). However listening to the line now, this  
sounds too loud to me. The person speaking sounds fine, but I've now  
got a large amount of background hiss coming thru. In order to get the  
"recommended" levels, most of my lines are in the range of +12.5, so  
I'm wondering if I'm just exceeding the ability of my Sangoma card to  
amplify the audio.

My TXGain's are all still at 0.0 as the Sangoma card didn't seem to  
want to let me adjust the gains. My levels are listing in the 5,000  
range, but it seemed no matter what I changed the values to, there was  
virtually no difference made to the audio levels. Listening to the  
transmit levels everything sounds fine.

What I am still getting is occasional static on the lines. Pops,  
squeaks, that kind of stuff. Sounds exactly like a handset cord is  
going bad, but it happens on any phone (and all have brand new handset  
cords). The person on the far end says they hear nothing wrong with  
the call. However, when I have asterisk record the call, the static is  
present on the recording. I also get the occasional robotic voice  
echoing back on anything said by the local person. That sounds like it  
should be typical echo on the line (I'm using a Sangoma A400DE with  
hardware echo cancellation). Everything I can find on echo and static  
tells me I should adjust my RX and TX gains.

So that brings me to my confusion/clarification. I've got my RXGain  
set to the "recommended" level, and my TXGain doesn't seem to be very  
adjustable upwards as it would appear to need based on the recommended  
levels. Could my static and echo be caused by my TXGain being too low,  
or possibly RX or TX actually being too high (since listening to the  
RX reveals lots of background hiss)?

I'm trying to work out this last little bit on my system as I'm  
getting grief that these calls have audio issues. I'm running out of  
things to check, so I'm looking for clarification on where exactly my  
RX and TX gains should be and which directions they will impact static  
and echo.

Thanks!

-chris
<www.mythtech.net>