Re: [vmeet] Comments on today's vMeet webex session

[Doug Otis <[e-mail]>]

On Apr 24, 2009, at 2:06 PM, Brian Rosen wrote:

> I believe your comment on the audio is incorrect.
>
> Let's say that no one has any echo cancel, and someone in the room  
> speaks. As you point out, you don't hear echo in the room.  The  
> remote participants would get the direct audio a bit later, and what  
> also happens is that some of the outgoing audio from the room  
> bounces off the hybrid in older phones and is reflected back to the  
> bridge.  The bridge has echo cancellation for this and the echo  
> won't come back to the room.
>
> When a remote participant speaks, the sound comes out the speakers,  
> gets picked up by the microphone a bit later, and is sent back to  
> the participant, delayed.  Most conference bridges can't actually  
> deal with this: they aren't equipped to have local echo.  In this  
> regard, it's not any different from two conference phones in use  
> with a phone connection between them.  If you don't do anything  
> locally, you WILL get echo.
>
> However, there are devices available that are designed to link the  
> room PA to the phone line used for the audio connection, and they  
> have the same kind of echo cancellation that  conference phone  
> does.  So, I think it will work out okay, although we have to make  
> sure we do that.

Local echo canceling equipment of this sort will cost much more than  
the suggested Net-Box used to project slide presentations.  Echo  
cancelation also seems unlikely able to deal with audio delays that  
that might exceed more than a second.  The IETF will be dealing with  
long distant participants and audio streaming systems handling many  
participants.   It would be much safer not to expect there will be an  
ability to offer a system able to provide rapid exchanges of remote  
and local speakers without some form of intervention.  No system is  
able to support everyone talking without also everyone following some  
type of cue.  Even a phone bridge suffers from this problem to some  
extent.  It really seems that the local room will need to decide when  
they wish to listen to a remote speaker/presenter.  This will be much  
as they do for someone at the microphone within the room, or for a  
presenter.  At that time, when the person is remote, there will be a  
need to mute the room's PA feed into the RMC (perhaps the audio input  
of the Net-Box), and then enable the RMC output into the PA, (perhaps  
the audio output of the Net-Box).  A Net-Box used in this manner could  
then offer high quality sound where there is no opportunity for any  
echo to be heard.

-Doug