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
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