Since there has been so much discussion of this technique, I thought
the following would interest everyone. The URL is
http://www.locationsound.com/proaudio/ls/tips/techtips8_7.html
I apologize in advance if this is just noise - I am definitely not a
microphone expert.
-- Chuck
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COINCIDENT OR "INTENSITY" STEREO TECHNIQUES COMPARED
Stereo recording for television in the U.S. has a potentially nasty pitfall
waiting for the unwary. The MTS format in the NTSC TV signal is not always mono
compatible. If non-coincident stereo recordings are used, they will cancel when
received in a mono TV set. The primary coincident techniques are XY, MS, and
Blumlein.
XY Cardioids and Hypercardioids:
XY uses a crossed pair of cardioids or hypercardioids. The cardioids are placed
at an angle of 90-120 degrees and placed fairly close to the sound source. The
angle for hypercardioids is typically more narrow to preserve a solid center
image. The increased reach of the hypercardioids allows for a more distant
placement.
With any stereo technique, the microphones should have as good a polar response
as possible and be closely matched in all aspects.
MS Stereo:
This intensity technique used a cardioid (the M or mid-component) pointed at
the source and a figure eight (the S or side-component) oriented laterally. The
outputs are combined in a sum and a difference matrix which converts the
signals to XY stereo [(M+S) and (M-S)]. The MS technique provides one major
advantage in that the ratio of the M and S signals can be changed in the matrix
to control the width of the stereo image. The only disadvantage is that the MS
signal is confusing to listen to while monitoring. Many modern mixers and
recorders have matrix decoders in the monitor circuits to overcome this problem.
=====
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Chuck Bragg, Pacific Palisades, CA
Membership Chair
Newsletter Editor
Santa Monica Bay Audubon Society:
www.smbas.org
========
________________________________________________________________________
________________________________________________________________________
"Microphones are not ears,
Loudspeakers are not birds,
A listening room is not nature."
Klas Strandberg
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