[asterisk-users] Question about echo cancelation

[Olivier]

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 ?


Consequence of having one direction EC, how can you help Alice if Bob is
local (ie Alice's media gateway and Bob's analog phone, for instance, are
connected to the same public switch) ?
In this case, you can't rely on any public EC system ?
As the one in your gateway is one-way (it seems to be the standard), the
only thing you can play with is to play with volume ... or is ther something
I'm missing ?


>
> Olivier wrote:
> > 2008/10/11 Eric ManxPower Wieling <eric at fnords.org>
> >
> >>
> >> Olivier wrote:
> >>> 2008/10/10 Eric ManxPower Wieling <eric at fnords.org>
> >>>
> >>>> All calls with a 2-wire analog piece have echo.  You cannot perceive
> the
> >>>> echo because it happens so fast on non-VoIP connections.  On VoIP
> calls
> >>>> you have significant extra latency while causes you you to perceive
> the
> >>>> echo.
> >>> Do you mean "generated locally" or "generated distantly" ?
> >>>
> >>> I understand that VoIP extra latency sometrimes renders perceivable
> what
> >> was
> >>> unperceivable before.
> >>> What suprises me is to hear that media getways "filter one-way only" :
> as
> >>> 2-wires analog devices produce echo, and every phone has 2-wires analog
> >>> audio, in every call you've got at least 2 sources of echo : one in
> each
> >>> endpoint.
> >> Where did you hear that media gateways "filter one-way only"?
> >
> >
> >>From a media gateway vendor (mentioning its own products capabilities).
> > That's the main reason I opened this thread as it surprised me a bit ...
> >
> >>
> >> Any 2-wire analog leg will be a source of echo.  Many, many, many calls
> >> do not have a 2-wire leg.
> >
> > Even in handset audio circuit ?
> > I was thinking that any handset is a potential echo source due to this
> audio
> > circuit ...
> > Do you agree ?
> >
>
> --
> Consulting and design services for LAN, WAN, voice and data.  Based near
> Birmingham, AL.  Now accepting clients worldwide. Contact me for Tellabs
> echo canceling systems.  Also see http://www.fnords.org/skillslist.html
>
> _______________________________________________
> -- Bandwidth and Colocation Provided by http://www.api-digital.com --
>
> asterisk-users mailing list
> To UNSUBSCRIBE or update options visit:
>   http://lists.digium.com/mailman/listinfo/asterisk-users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.digium.com/pipermail/asterisk-users/attachments/20081012/a0b0da4b/attachment.htm