[Asterisk-Users] How to deal with echo in MeetMe?

[steve at daviesfam.org]

On Mon, 21 Nov 2005, Tony Mountifield wrote:

> I have a customer who is running fairly large conferences (between 5
> and 30 participants) on their Asterisk box. It uses SIP to talk to a
> PSTN provider.
> 
> They are complaining that under some circumstances they experience
> echo of one or more participants. On listening in to one of their
> conferences, it seemed to me that the echo was being introduced
> via the microphone of a couple of specific participants, as it was
> possible to eliminate this echo by muting those participants.
> 
> On discussing the participants' environments with the customer, it
> would appear that the problem occurs when participants are using
> speaker phones and there are multiple participants in proximity to
> each other, such that one participant's phone can hear the audio
> from that of another participant in the same conference.
> 
> It's my supposition that any echo canceller is going to have
> difficulties correcting for that scenario. Am I correct?
> 
> The problem I have is that the customer insists that their existing
> conferencing supplier (whom our kit is supposed to replace) does
> not suffer from this echo, in the same participant environment.
> 
> I am assured by our PSTN supplier that there is full echo suppression
> on the PSTN lines. Am I correct in believing that further echo
> suppression is neither possible nor required at the SIP interface
> within Asterisk?
> 
> Any advice on how to approach this would be appreciated.


Hmm,

That's a difficult one to resolve.  I presume that the existing 
conferencing system has low latency and therefore the crosstalk is 
not noticable.

Your solution is using a remote SIP provider - that will mean higher 
latency.  Meetme adds some too.

Moving from a remote SIP provider to PSTN to a locally connected PSTN 
would reduce the latency, whether it would be enough to avoid the effect 
I'm not sure.

Perhaps we could also add a fairly brutal "noise gate" into Meetme which 
mutes off all but the loudest participant or participants; not sure what 
that would sound like, but it would probably hide the crosstalk...

I do think that a bunch of speakerphones that can hear one another, all 
connected into a conference bridge with latency is an impossible echo 
cancellation task.  So either the latency needs to be removed or an echo 
suppression approach needs to be taken.

Steve