[AG-TECH] Echo canceller

Ed Ritenour erritenour at lbl.gov
Mon Jul 21 16:43:34 CDT 2003

Whether its one mic or fifteen or wireless or cables everywhere, the main
point is that you have good echo canceling. Someone said it earlier, because
it happens a lot, all it takes is one site with poor audio and you just wasted
a lot of peoples time. Also remember if you use more than one mic its is a
good idea to be able to mute the remaining ones, otherwise you do get
background noise, such as people rustling papers, typing on a laptop or just
a squeaky chair. Audio is what makes a meeting, without you may as well go
home. Skimp on PC's and projectors, but invest wisely on audio.


Don Lewis wrote:

> 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
> http://www.telex.com/Intercoms/products.nsf/pages/Eartubes
> 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.
> rich

Ed Ritenour                                                         Phone:
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Network & Telecommunications Department         Fax: 510-486-7000
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