[AG-TECH] Echo canceller

Richard Naylor richard.naylor at citylink.co.nz
Fri Jul 18 22:12:59 CDT 2003

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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