[Asterisk-Users] echo cancellation: the never-ending quest for truth

[Rich Adamson]

> Asterisk apparently has five echo cancellation algorithms: STEVE, STEVE2,
> MARK, MARK2 and MARK3.  The current default appears to be MARK2.
> 
> My question is, has anyone had any experience with any of the others
> (other than MARK2), and is there some conventional wisdom as to when to
> use one over another?

Most of those were variations that attempted to address echo issues with
the old x100p card. If you look at the source code dates, none of those
have really been touched in well over a year.

According to Steve, the echo cancellation algorithms do not have a very
wide operational range, and as a result its not all that difficult to find pstn
situations were the echo characteristics fall outside the usable ranges.
Its basically a trial & error test to see which one works the best given
"your" pstn line characteristics. Your neighbors line characteristics
may be completely different.

Following Mark's echotraining=800 changes around June 2004, it seems
most echo problems were minimized, and there hasn't been any list
activity relative to those algorithms since then.  Those that still had
objectionable echo found that swapping motherboards cured their issues.
That seemed to be related to interrupt latency and/or pci bus controller
chip problems that are apparently well known to those that work heavily 
with audio applications.

Rich