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Posted by Smarty on 04/22/07 19:22
The laws of physics don't really need to be violated so much as cleverly
exploited. There actually is a method to cancel mechanical sounds at a fixed
location removed from the source of the noise, and this method, "active
noise cancellation" is particularly suited for this problem, since the noise
is narrow banded and the microphone is a fixed location geometrically from
the noise source (the camcorder tape transport). Some of the applications of
this technology are in noise canceling headphones, microphones, electronic
mufflers, and noise abatement systems for controlling highway noise.
The design uses a replica of the offending noise, an equal amplitude but
opposite phase sound to arrive at the place you want cancelling to occur. In
this case the camcorder would have a small speaker creating this
cancellation signal driven by the proper energy placed to ensure the
coincident arrival of both the real noise and the cancellation signal at the
camcorder microphone.
This method was "invented" in the 1950s or 1960s at the University of
Darmstadt Germany, and was cleverly exploited in some high end audio gear
under the names of "Sonic Holography" from Phase Linear / Carver Corporation
as well as from another company called Sound Concepts. Bose and others have
also been using versions of it, as has the US Air Force in F16 cockpit
systems.
Smarty
"Mike Kujbida" <kXuXjXfXaXm@xplornet.com> wrote in message
news:591c8rF2iu9qsU1@mid.individual.net...
> jazu wrote:
>>> 1. It is not physically possible to "resolve" the "problem" of
>>> sounds produced by mechanical devices a few mm away from a microphone.
>> C'mon, they put man on the moon, so they could fix it too.
>> The problem is why they install mic soo close? They could design some
>> kind of external mic (without mic plug) on the top of camcorder.
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