[Asterisk-Users] Fun with Echo

[Steve Underwood]

Andrew Kohlsmith wrote:

>On Monday 12 June 2006 17:55, shadowym wrote:
>  
>
>>Believe me, you can drive yourself insane trying to come up with some
>>magical formula that JUST works because it usually won't happen that way.
>>Software echo cancellers are simply not good enough for many situations.
>>    
>>
>
>Actually that's untrue.  I think (hope) that Steve Underwood will jump in here 
>and correct me, but it's my understanding that the only real reason why the 
>software echo cancellers available in Zaptel don't work as well as the 
>hardware echo cancellers from Tellabs and the Octasic chips in the Sangoma 
>and Digium hardware echo cancellers is because of implementation.  
>
>There is a spec for echo cancellation on PSTN called g.168.  I believe it's a 
>suite of tests which put the echo canceller through its paces and if you pass 
>them you are certified to conform to g.168. None of the echo cancellers in 
>zaptel conform to this, whereas the Octasic, Tellabs and other hardware echo 
>cancellers all do.  If someone were to put the effort and energy into making 
>the software echo cancellers compliant, you should find similar results to 
>the hardware echo cans.
>
>The echo cancellers in Zaptel are far better than anything I could throw 
>together myself, and there's a lot of heavy math and dark juju hiding inside 
>that optimized code, but they're all still very much proof of concept and 
>test code compared to a true g.168-compliant echo can.
>
>Basically they're there for free and might get you what you need, but they're 
>certainly not a reflection of all that is possible with a general CPU echo 
>canceller.
>  
>
Since you invited me, see http://www.soft-switch.org/dumb-vs-smart/ar01.html

Steve