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Re: <00> Sound Cancelation

From:
Date: Thu, 3 Dec 1998 06:42:38 -0600 (CST)

> > is it at all posible to write some software that would help drown out
> > natural sounds and heihten important ones like conversations.
> > 
> > I know that the people at the hearing aid companies have been working
> > on this sort of thing for a while.
> 
> I've had thoughts about this, but I think it would be much simpler/work
> better to do it with hardware...
> 
> ie:  Put a highly directional microphone (mic1) in front of your mouth,
> and second omnidirectional mircophone (mic2) on your
> shoulder/back/chest/topofhead...  Then use an op-amp wired in a
> subtractive sort of way to remove the waveform of mic2 from that of
> mic1, if you get my drift.

It sounds like what you're describing would only work for the wearer. In
other words, a noise-cancelling mike. These are commercially available,
although they work a little differently from what you describe. They are
basically open on both sides of the element, so the user (usually a pilot)
talks (applies sound pressure) to only one side of the element, while any
other sound (engine/cockpit noise, for example) hits both sides of the
element equally, and doesn't register. Or at least that was the theory as
described to me in flight school.
The only problem with these mikes is that they are not very senstive, and
you literally have to hold one up to your mouth close enough that your lips
brush it.

Paul Archer

----------------------------------------------------
A key to the understanding of all religion is that
a god's idea of amusement is Snakes And Ladders with
greased rungs.   -- Terry Pratchett, "Wyrd Sisters"
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