[AG-TECH] AG Echo problems

Ben Juby bpj00r at ecs.soton.ac.uk
Wed Feb 20 09:42:23 CST 2002

[apologies to everybody on the ETF-ACCESSGRID list if you have received
this twice. Mike quite rightly pointed out that this would be more
appropriate for the AG-TECH list]

In an AG test session yesterday it appeared that we were causing some
echo when we unmuted our mics and other sites spoke to us (the other
sites said they could hear their own audio being fedback through our
mics). We have so far been unable to determine why this is and we would
welcome any suggestions as to what is going wrong.
I have attached a screenshot of the Gentner matrix we have been using
here. Our setup is a mono one. The Genelec monitors connect to outputs C
and D (with identical audio going to each). Output 1 is the ghost output
used for echo cancellation, though since this is a mono system I guess I
could have got away with just using output C or D as the echo cancellation
channel. Currently we have been using it with only 2 mics connected (Mic
1 and 2) and there is nothing connected to the inputs for Mic 3 and 4.  

I've double checked that echo cancellation is turned on internally in our
Gentner, as I know there is a global setting that can be used to disable

After the test cruise yesterday Don Cruickshank and I did some audio
testing by setting up a RAT session from our AG room to Don's desktop PC
(Don used a headset to avoid causing feedback at his end). When Don spoke
he could clearly hear an echo as his audio fedback into the mics in our AG
room. When I disabled echo cancellation in our Gentner, Don said that the
echo got far more pronounced. So it appears that our echo cancellation is
working to a degree, but not as well as it should be.    

We currently have very high levels of background noise in our AG room from
all the fans in our rack. Is it possible that all this background noise
could be causing the echo cancellation to work less efficiently?



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