C Source for VoIP Echo Cancellation

Hi everybody,

Does anybody know any C source code for Echo Cancellation on a voice over
ip system?

Regards,

M. Hafezi

Does VOIP have some innate need for echo cancellation?  Or is the echo that 
needs to be cancelled just the acoustic echo of a speakerphone-type system that 
happens with any communications link?  I would think the latter, since with VOIP 
the transmit and receive signals are electrically independent no (as opposed to 
one a phone where there both sides go down the same twisted pair)?

-- 
Jon Harris
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"MMHafezi" <MMHafezi@Gmail.com> wrote in message 
news:f8CdnfSVrt4cXhzenZ2dnUVZ_v2dnZ2d@giganews.com...
>
> Hi everybody,
>
> Does anybody know any C source code for Echo Cancellation on a voice over
> ip system?
>
> Regards,
>
> M. Hafezi 

Hi Jon,

Jon Harris wrote:
> Does VOIP have some innate need for echo cancellation?  Or is the echo that
> needs to be cancelled just the acoustic echo of a speakerphone-type system that
> happens with any communications link?  I would think the latter, since with VOIP
> the transmit and receive signals are electrically independent no (as opposed to
> one a phone where there both sides go down the same twisted pair)?

Often the 'last mile' of a VIOP link is to a 2 wire phone. The echo is
normally caused by the less-than-infinite transhybrid loss.

Regards
Robert

Hi Harris,

Thanks for your reply. No, the echo is not from speakerphone. In fact, one
side, is over ip while the other side is on a common two wire phone line.
Actually, the voice from the talker on computer side passes a local area
network and feeds a hardware that converts the signal to analog and puts
it on a two wire phone line, here a return signal feeds back to the D/A
and through the network comes back to talker and because of the long delay
it is very disturbing.

Now, I want to develope an Echo Canceller software on computer side to
cancel this echo. I should emphasize that on computer side I just have
access to sent and received buffers of voice samples.

I really appreciate any hint from you.

regards,

M. Hafezi

>Does VOIP have some innate need for echo cancellation?  Or is the echo
that 
>needs to be cancelled just the acoustic echo of a speakerphone-type
system that 
>happens with any communications link?  I would think the latter, since
with VOIP 
>the transmit and receive signals are electrically independent no (as
opposed to 
>one a phone where there both sides go down the same twisted pair)?
>
>-- 
>Jon Harris
>SPAM blocker in place:
>Remove 99 (but leave 7) to reply
>
>"MMHafezi" <MMHafezi@Gmail.com> wrote in message 
>news:f8CdnfSVrt4cXhzenZ2dnUVZ_v2dnZ2d@giganews.com...
>>
>> Hi everybody,
>>
>> Does anybody know any C source code for Echo Cancellation on a voice
over
>> ip system?
>>
>> Regards,
>>
>> M. Hafezi 
>
>
>

Have a look at Asterisk.

John

Jon Harris wrote:
> Does VOIP have some innate need for echo cancellation?  Or is the echo that 
> needs to be cancelled just the acoustic echo of a speakerphone-type system that 
> happens with any communications link?  I would think the latter, since with VOIP 
> the transmit and receive signals are electrically independent no (as opposed to 
> one a phone where there both sides go down the same twisted pair)?
> 
VoIP has a very serious need for echo cancellation. Because of the 
latency in VoIP connections, any echo from a hybrid on a PSTN 
interconnect - even earpiece to mic coupling in a handset - becomes a 
seriously annoying echo. In normal PSTN work these things merely give a 
little pleasant reverberation. VoIP is just the same in this regard as 
digital cellular systems, which also have a very strong need to 
eliminate echoes before signals pass across the high latency section of 
the path.

Steve

Thanks, Steve, Rocky and MMHafezi for excellent explanations.  From my own 
experience, I knew that echo cancelling was more critical (and the echo more 
annoying) with longer delays, but didn't put all the pieces together, especially 
the fact that VOIP may involve 2-wire POTS.

To the OP, I can't help with C source other than to suggest a Google search as I 
think I've seen similar questions pop up here before.

-- 
Jon Harris
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"Steve Underwood" <steveu@dis.org> wrote in message 
news:dm227d$88m$1@nnews.pacific.net.hk...
> Jon Harris wrote:
>> Does VOIP have some innate need for echo cancellation?  Or is the echo that 
>> needs to be cancelled just the acoustic echo of a speakerphone-type system 
>> that happens with any communications link?  I would think the latter, since 
>> with VOIP the transmit and receive signals are electrically independent no 
>> (as opposed to one a phone where there both sides go down the same twisted 
>> pair)?
>>
> VoIP has a very serious need for echo cancellation. Because of the latency in 
> VoIP connections, any echo from a hybrid on a PSTN interconnect - even 
> earpiece to mic coupling in a handset - becomes a seriously annoying echo. In 
> normal PSTN work these things merely give a little pleasant reverberation. 
> VoIP is just the same in this regard as digital cellular systems, which also 
> have a very strong need to eliminate echoes before signals pass across the 
> high latency section of the path.
>
> Steve