[Asterisk-biz] Bottom line on echo cancellation for Digium and Sangoma cards

[Andrew Kohlsmith]

On Wednesday 16 November 2005 04:02, smbPBX wrote:
> So where does this leave TE110P and TDM400P? I have read much about echo
> problems with Digium cards.

Neither will have on-board echo cancellation hardware.

> So, with echo cancellation, are TE110P and TDM400P unsuitable for business
> applications? Even more confusing to me to introduce the latest TDM2400
> with and without echo cancellation. Again, is the one without echo
> cancellation unsuitable for business applications?

You don't need on-board hardware echo cancellers for business applications.  
I'm certainly not using any.

> Now, moving on to Sangoma. I was always led to believe that Sangoma cards
> were much better at echo cancellation than Digium.
> Until...I read their announcment of A104D with hardware echo cancellation.
> So does this make A104U as well as A102U and A101U unsuitable for business
> applications?

Again, hardware echo cancellation does not business-class hardware make.  
There is absolutely nothing the hardware echo cans can do that the software 
echo cans can't, except save you CPU use.  

That's it.

Can you explian what it is you *have* done to eliminate echo?  Have you 
actually methodically measured and tuned your gains, tried the various 
software echo canceller options and tuned the system, or have you slapped 
some values in that other people say worked for them and threw your hands up 
in frustration as you adjusted values without any idea of what they were 
actually doing?

I've seen many, many people do the latter, claiming they've "properly" tuned 
the system and echo still remained.

> So, what is the bottom line on echo cancellation with these cards?

The bottom line is that software echo cancellation works very well so long as 
you work within the constraints of the system.  The echo canceller add-on 
does a fine job too, in addition to reducing overall CPU use, but again: only 
within the constraints of the system it was designed.  Sangoma's echo 
canceller hardware is quite a bit more robust than Digium's from my 
understanding (far longer tail lengths, and able to cancel echo in both 
directions) but again...  If your particular brand of echo falls outside the 
design spec for the hardware or software, they will *all* fail miserably, 
just as a DS3 shelf full of echo cancellers would if you misapply them.

-A.