iaxmodem connection failures | testing custom gain in Asterisk

Hi All,

I am hoping someone can help shed a little light here...

I've been using IAXmodem happily for a long time now but recently 
something changed out in the wild and my modems can no longer correctly 
detect silence or train - particularly when going off-net to PSTN and 
vice versa.

So all of a sudden, a 3% failure rate became a 97% failure rate across 
the board for all deployments in different locations throughout the 
city. (I am in Adelaide South Australia)

I've done a lot of investigation and what I suspect has happened is that 
an interconnect hardware change has occurred at the wholesale PSTN 
transition to on-net causing either noise on the lines OR low gain and 
poor signal to noise.

I've had a go at boosting the TX and RX in Asterisk using a custom 
context but I'm not sure its actually doing anything... What I have 
tried to do is use iaxmodem to record the modems conversation with and 
without the boost and inspect the different waveforms but I can't see 
any difference in the gain (had to use sox to convert the RAW to WAV so 
i'm not sure if sox in Debian normalises by default.

So...
Can IAXmodem report gain for each side of the conversation?
Is there a method external to Asterisk to improve SNR or up the tx/rx gain?


Cheers,

Nathan



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