[AG-TECH] Echo canceller

Don Lewis djlewis at ualr.edu
Mon Jul 21 14:58:50 CDT 2003

Sorry to butt in Rich but you are makeing very good points.
I have been considering a mic like the Shure m58 you mention.
I have seen other sites with large AG rooms using a hand mic
with good success. The main problem seems to be passing the mic.
Has anyone had negative results with the hand mic method? Our
AG room is too large for long throw mics to work effectively
without feedback or excessive echo.

thank you,
Don Lewis

-----Original Message-----
From: owner-ag-tech at mcs.anl.gov [mailto:owner-ag-tech at mcs.anl.gov]On
Behalf Of Richard Naylor
Sent: Friday, July 18, 2003 10:13 PM
To: bernholdtde at ornl.gov; Stuart Levy
Cc: ag-tech at mcs.anl.gov
Subject: Re: [AG-TECH] Echo canceller

At 11:24 a.m. 18/07/2003 -0400, bernholdtde at ornl.gov wrote:
>On Fri, 18 Jul 2003 09:21:44 -0500  Stuart Levy wrote:
> > equip all meeting participants with low-gain headset mikes?  It'd be
> > a little clunky, but probably not too uncomfortable if the
> > participants didn't move around too much, so their wires wouldn't
> > get tangled.
>It would be interesting to see if you could make use of some of these
>Bluetooth headsets they're making for cell phones...

I think they would work depending on the sensitivity of the mics. The rule
of thumb for stage work is that an open (ie live) mic should be as close to
the speaker as possible and the nearest other mic should be at least twice
as far away. WHich is why you often see a singer with the mic on their
lips. Mics like the Shure sm58 are designed for this. This close mic-ing is
done to try and keep mics isolated from other sounds such as fold back
speakers, other singers, the drummer etc. Acoustic baffles are also used
(persex sheets to baffle the sound).. So if the blue tooth mic was an omni
design and quite sensitive it would pick up other sounds and prbably the
speakers with the content from the remote end.

But having the remote audio only on the headset would stop the feedback
loop, and so it would work.

At a radio studio the announcer wears a headphone so that any sound they
hear like a talk show ring in, doesn't get picked up by the mic. Equally a
"mix-minus" signal is sent to the person who phoned in. Mix-minus is the
station signal minus their own audio. The phone or its hybrid gives the
phone caller enough of their own audio.

At a TV studio, you use a small ear piece (typically the Telex tube
which is hidden from view and a lapel mic. This keep the audio apart and
avoids any echo at all.

So if I had to make an AG node without Gentner and speakers, I'd just wire
a headset amp behind the couch/sofa and lapel mics on everyone, and it
would be fine.

So the Bluetooth headset will work, if you turn off the speakers in the
node room.

In terms of my problem, the single channel echo box vs teh 4 channel
Gentner, I think I'll build one of each. The single channel will work
depending on how I place the mics in the room. The main point is that in an
AG I don't think you want invasive technology, like the way we have to wire
up the clothing of talent in a TV studio.


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