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Re: parabolic T mic and phase invert noise reduction

Subject: Re: parabolic T mic and phase invert noise reduction
From: Rob Danielson <>
Date: Fri, 31 Dec 2004 11:07:14 -0600
Neat Trick. I think the 183's are sounding pretty nice. So is the
theory the dish shapes frequency response and these frequencies are
getting phase cancelled out or is it an ampltiude difference? Can you
run through how this works again? It seems like part 3 shows
something like a -6dB roll-off starting at about 700hz.  The  distant
machine is centered around 240 hz. Do you think pt 3 is effectively
cancelling more in this Hz area? For a stereo result, attentuation in
the 240Hz area seems to help bring out the spatial image and improve
overall clarity. Your caps show a similar zizzz noise concentration
~8KHz-- maybe a few hundred cycles higher than mine. Rob D.

>Still working with the parabolic mic configurations.
>Rough photo and sound to illustrate only.
>
>As a hybred between barrier and a no barrier stereo mic method used in
>parabolic dishes, I constructed a T mic using the 183 elements.
>
>Pictured without foam wind screens as seen through the dish.
>http://home.comcast.net/~richpeet/q1t.jpg
>
>Sound when focused at bird seed on the ground with quiet visiting
>redpolls and pine grosbeaks at about 100feet. Note the sound of the
>logging equipment a few miles away.
>1.5 meg download
>http://home.comcast.net/~richpeet/183t.mp3
>
>First segment of three is the raw stereo track.
>
>Second segment is a mono track made by combining the two stereo channels.
>
>Third segment is a mono track with one channel phase inverted prior to
>combining the two stereo tracks.
>
>I thinik it does a pretty good job of reducing the logging background
>noise. Of course it can not reduce the background noise more than the
>actual gain of the dish itself.
>
>Rich
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>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
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>


--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee


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