[asterisk-users] Question about echo cancelation

[Tilghman Lesher]

On Sunday 12 October 2008 04:15:02 Olivier wrote:
> 2008/10/11 Eric ManxPower Wieling <eric at fnords.org>
>
> > Handsets use a 4-wire connection.  Handsets with the the volume turned
> > up could cause a form of echo as the microphone picks up the ear piece
> > audio (I call this acoustic echo).  Everything I said applies to 2-wire
> > caused echo.  Other types of echo is fairly uncommon and cannot be
> > solved by normal echo canceling systems.
> >
> > Most echo canceling systems I've seen (mostly tellabs) only cancel echo
> > in one direction.
>
> Which one ?
> Using previous example, I would say they cancel Bob's voice echo ...
> Said differently, echo canceller would filters out from outgoing audio
> signals matching signals previously heard in incoming audio (Bob's voice).
>
> > I suspect all of Digium's EC systems only do echo
> > canceling in one direction as well.
>
> Is anyone aware of EC systems working in both directions ?

Pray tell, how do you echo cancel in both directions?  Wouldn't that
necessitate cancelling echo before it occurs on the line (sort of a white
noise/pink noise kind of operation)?  Seems like modelling a projectile such
that when it reaches its target, the atmospheric stresses during its flight
turn it into a perfect sphere (and with about the same likelihood of success).

-- 
Tilghman