[asterisk-users] Question about echo cancelation

[Eric "ManxPower" Wieling]

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.  I suspect all of Digium's EC systems only do echo 
canceling in one direction as well.

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 ?
>

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