[Asterisk-Users] Echo cancellation

[Nicolas Gudino]

This is indeed an excellent paper. And I learned something I didnt know, and
it may clear things up to people who dont have the time to read the whole
article:

"The role of the echo canceler is to remove the echo portion of the signal
coming out of the tail circuit and headed into the WAN"

I point this out because I thought that the function of echo cancelation was
the oposite (remove echo coming in).

Also from this paper, if you want to test if echo cancellation is working at
the other end:

"The quickest way to determine if you have a working echo canceler in the
circuit is to make a call and immediately begin to say something like "TAH
TAH FISH" repeatedly. The person on the other end of the line should be
silent. If you are calling a voice-mail system, wait for the announcer to
stop talking before starting the experiment.
If the terminating tail circuit has cancelable echos and if the echo
canceler is enabled, you will hear echo for the first few utterances and
then it will die away. After a few seconds of speech, the echo should be
gone or at least very quiet compared to the echo level at the beginning of
the call. This is the signature of a working echo canceler. "

This really is a great article, and everyone having echo issues should read
it. Thanks Richard!

----- Original Message ----- 
From: "Richard Scobie" <r.scobie at clear.net.nz>

> According to the excellent Cisco paper "Echo Analysis for Voice over
> IP", which the Wiki links to at:
>
>
http://www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a00800d6b68.shtml
>
>
> "Headsets are particularly notorious for poor echo performance.". This
> is due to lack of acoustic isolation. Perhaps you could test using
> headphones and a mic.
>
> After reading the above paper, I was able to tune my setup and make a
> significant improvement. Given the high number of questions about echo
> on the list, it would almost be worth including the link to it as a
> file, "README.echo" in the source.
>
> Richard