Asterisk and the big bad echo

Corey Edwards tensai at
Sat Sep 24 00:57:47 MDT 2005

On Fri, 2005-09-23 at 19:17 -0600, Gabriel Gunderson wrote:
> Echo is the #1 problem with any install of Asterisk that I have done.
> Echo has many potential causes but is basically side-tone that is
> delayed to the point that it is occurring perceptibly later then your
> voice.  It is always the near side (your voice) that you hear coming
> back at you.  The other party never notice anything.  This side-tone is
> good for letting your users know how loud they are talking but really
> causes more pain then good.

Echo sucks. I would agree that it's the #1 problem with all of my
Asterisk installs so far. That's only been two, mind you. My box at home
works great. The one at work echos on every single line and in every box
I've tried. I did all sorts of stuff to try to eliminate it and nothing.
I even went so far as to wire in some different size resistors hoping to
fix the impedence imbalance, but no go. I think my work machines may
just be jinxed.

>   So, I want to know, is there a way to tell
> asterisk that I don't want *any* side-tone?  Just drop it and the
> potential for echo goes with it.  What have you all done for this?

Not with an analogue phone line. The problem is send and receive are
done with the same pair of wires. No way to know for sure where each
volt came from. I suppose you could eliminate echo completely by not
talking. :)

Now with a T1 or other digital lines it shouldn't ever be a problem.
Same would be true for VoIP channels. It's really only where you connect
to analogue lines, so whereever you can eliminate those will be a bonus.

For the truly annoyed, AdTran makes some hardware echo cancellors. They
sit inline to the POTS line and from reports I've read work quite well.
I don't have anywhere near that kind of $$$ to try it myself though.

For me, I think I'll be switching to a VoIP provider at some point.
NuFone looks pretty good for an Asterisk provider. Simple IAX connection
and no-nonsense pricing. No commitment either. Perhaps Hans would like
to chime in with his experience.


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