[Asterisk-Dev] Echo Canceller assistence (SteveU?)

[Richard Scobie]

Steve Underwood wrote:
> The current echo cancelers have no protection against serious drift on 
> narrow band (e.g. single or dual tone). The current cancelers fail 
> almost every test in G.168.
> 
> No amount of minor tweaking will deal with this. If requires a proper 
> narrow band detector to fix it. Several possibilities for this exist - 
> Autocorrelation, AMDF/ASDF, Teager-Kaiser energy operator, etc. In 

Thanks for confirming the conclusion I had come to after a head spinning 
couple of weeks reading various papers.

> Suppressing adaption as you suggest helps a bit, but if someone presses 
> a DTMF key at the wrong time things still fall apart. A narrow band 
> detector is an essential element of a robust detector. It does increase 
> the compute requirements, though.

I take your point, but as a short term fix for the narrow case I have 
outlined (busydetect failure), freezing the canceler seems, (speaking as 
a non-coder), a simple fix.

This busydetect unreliability is the only thing now stopping me 
recommending the TDMs for production in situations where disconnect 
supervision is unavailable.

Regards,

Richard