STEREO RECORDING TECHNIQUES FOR TV & MOTION
PICTURE
by Edwin J. Somers, CAS
This is a study on stereo recording
techniques as applied to the television and motion picture
industries. When recording in stereo for motion pictures
and television, it is advisable to use coincident techniques.
The method of transmitting stereo audio in the NTSC
television format currently used in the United States
is very unforgiving of non-coincident stereo. Simply
put, spaced stereo recordings are not mono compatible.
Audio tracks recorded with spaced stereo microphones
will cancel when received by a monaural television set.
Coincident techniques use microphones
arranged close together. Often in the same housing,
they include Blumlein (crossed pair of figure of eights),
M-S (Mid-Side), and X-Y (cardioids set at a 60-120 degree
angle). The most popular coincident stereo techniques
are X-Y and M-S. The angle of the cardioids in the X-Y
pattern determines the width of the stereo image. Mid-side
is an interesting method where a cardioid is used for
the mid or forward-facing microphone, and a figure of
eight or bi-directional is used for the side-facing
microphone. The signals from the mid-side pair are routed
through a summing matrix before or after recording.
By adjusting the ratio of the side to the mid signal,
the stereo image can be widened or narrowed as desired.
It is easy to understand why this is desirable in post-production
where the dubbing mixer can change the stereo image
to suit the picture.
