[asterisk-users] 1.8.3 - IAX - echo - jitterbuffer

[Dave Platt]

> I'm using iaxagent on a Droid X to connect by IAX to 1.8.3 at the 
> office. 1.8.3 has sip phones. The audio is fine on the Droid X side. On 
> the office side, they hear an echo of _their_ speech, not mine.
> 
> The office uses sip-providers generally without any echo problem.
> 
> Where do I start to figure this out? How do I narrow it down? Can I 
> figure out if it is an iaxagent problem? Could using jitterbuffer cause 
> this?

One thing you must consider, is that this echo they're hearing
may be entirely an acoustic one, within (or around) the Droid
itself.

It's very possible for the microphone in a handset to
pick up sound being emitted by the handset's speaker.  This
acoustic feedback can occur within the handset itself (sound
from the speaker "leaks" through the chassis of the handset and
reaches the microphone from behind), via mechanical coupling
through the handset body, or by the mic picking up the sound
from the outside (after it has come out of the speaker
into the air).

The best way to determine whether this is the case, is
probably to shut down the speaker and isolate the mic...
plug in an earphone which has a separate mic on its cord,
and see if the callers still report the echo.  If they do,
it's due to electronic or digital goofs somewhere, but if they
do not, it's due to acoustic feedback at the handset.

There are (in principle) three ways to reduce or eliminate
the echo:

-  Damp it out physically - block the acoustic feedback
   pathways.  In a small USB phone handset I have, I found
   it necessary to "stuff" the open spaces inside the handset
   with cotton and foam, to block the back-wave from the speaker
   before it reached the microphone.

-  Use software which has some sort of VOX (voice-operated
   switch) detection or squelching... so that when the sound
   level at the microphone is less than you'd get by speaking
   into the mic, the handset "cuts off" the mic audio pathway
   entirely, and sends only silence (or sends nothing at all,
   although Asterisk doesn't always deal gracefully with this).

-  Use a better handset.