[asterisk-dev] Zaptel Echo Cancellation

[John Lange]

On Thu, 2006-08-03 at 13:27 -0400, Andrew Kohlsmith wrote:
> On Thursday 03 August 2006 12:49, Hans Petter Selasky wrote:
> > Hardware echo cancellers perform no better than software echo cancellers.
> > What you need is good timing and ringbuffers. Then you compute exactly how
> > many bytes are in the buffer, and just "skip" those before doing any echo
> > cancelling. In this case the buffer delay does not matter at all. For
> > example I have 50ms buffering working very well with 32ms echo-cancelling !
> > You might think this was very difficult and ureliable, but no. All you need
> > is a ring buffer, and a good timing source.
> 
> That's the best explanation I have heard and yes, it makes perfect sense now.  
> So long as the buffer size doesn't change without the echo canceller knowing 
> about it it makes very little difference.

What the heck does all that mean? ;) A good timing source and a
ringbuffer?

I'm fairly clueless on echo canceling but I'd sure like to read up on
it. Is there some links someone could recommend? I've already read most
of whats on the voip-info wiki but it does not get into the nuts and
bolts of how echo cancelers are implemented.

I've tweaked the crap out of the settings that are available in Asterisk
and simply can not eliminate echo to the point where its not noticeable
to users so now I'm ready to take more drastic steps if I only knew what
the heck I'm doing.

John