I was having some horrible echo on PSTN calls. It took me ages to locate the problem and the solution -- it was my SPA3102.
I just thought I'd post this here, because this seems to be a simple solution when you know what you're doing, and I hope it helps others find the solution more quickly.
- The echo canceller in the SPA-3000 is very basic and limited to an echo tail length of 8ms. It may take 15-30 seconds for the SPA-3000 to "converge" on the proper cancellation values for a call. Long PSTN loops or cellphone calls may suffer from uncorrectable echo with an SPA-3000, in which case the only solution is to buy an FXO gateway with a better echo canceller. - bani
- Echo Supp Enable (PSTN Line) may produce very poor quality PSTN calls, as this setting dynamically adjusts gain based on sending and receiving audio levels. Volume may jump around and callers may find their sides being squelched in a CB-halfduplex-style. If you are willing to tolerate some echo while the SPA-3000's echo canceller converges during a call, you can disable this for much better overall PSTN call quality. - bani
- In many cases the outgoing PSTN audio (SPA To PSTN Gain) is "too hot", leading to distortion that no echo canceller is able to handle. Lowering this by several db may help alleviate some PSTN echo issues. -6 is a value which works well for me. - bani
The thing that worked for me was the SPA to PSTN gain. The default was 0. I set it to -6 and Bob became my uncle.