[Asterisk-Users] Echo problem on SPA-841

[Robbie Hughes]

I'm running the latest firmware on the SPA-841 and have a problem  
with echo.
The echo occurs on all calls (PRI ISDN on a E110p or SIP) and is not  
present when I use the SNOM190 phones so I can def. isolate it down  
to the SPA-841s. The codec used is g711u and the phones are on their  
own dedicated 100mbit switch with no other traffic. The server is a  
3Ghz PIV sitting at 99.9% idle all the time.

Specifically, i believe I am getting feedback from the headset  
speaker to the microphone, although the problem is also apparent on  
the headset (do not have a selection of headsets to try so cannot  
draw any conclusions from this)

The echo can be cured (or at least mitigated) by turning down the  
volume on the headset/handset speaker, though at this point the  
callee struggles to hear the caller. If i turn down (or even leave  
the gain at 0 from +6) the microphone on the headset/handset then the  
caller cannot hear the callee (callers complain that the callee  
sounds far away - 'have you moved to bangalore' is the usual comment 
(!) -, though the echo is better attenuated.

Using the Echo() application I can examine the feedback pretty  
closely by using DTMF tones. In order to stop the echo, I simply push  
mute and it vanishes instantly. It is otherwise damped in a time that  
appears to be a function of the amplitude of the noise made -  
predictably enough...

Short of treating the symptoms, does anyone know of a better way of  
solving this problem? Is there an echo cancellation algorithm for SIP  
traffic, for example? Failing that, does anyone want to buy 50 boxed  
hardly used spa-841s - one careful owner...none thrown against the  
wall in anger...yet ;-)