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Three and four microphone techniques are generally an extension of the
other methods already discussed, therefore, most of the characteristics,
advantages and dis-advantages apply. The most successful means to employ
three and four mic techniques is to setup a primary pair of microphones
and a secondary or accent pair of mics. These secondary mics should be
used to augment the sonic character of the primary pair.
A center channel
Omnidirectional mic used with a 90 degree x-y pair of hypercardioid mics
will produce a recording that is more open, with a more natural and extended
bottom two octaves. This third microphone should be in the same vertical
plane as the primary pair, this reduces time and phase differences between
mics and allows for better high frequency response (out of phase = dull ).
If great care is not taken with mic placement a noticeable degradation at
high frequencies occurs, producing a dull, transient poor sound. The level
of this third microphone should be about 9 to 20 dB below the primary pair.
If a phase monitor oscilloscope is used a rearward spacing of the third
microphone yielding an in phase time delay of 15 to 20 microseconds can
produce very good results. This third, delayed microphone , has the effect of
opening up the soundstage allowing for better delineation of vertical spacial
information.
Using Four microphone techniques it is much more difficult to achieve
desirable results. The time and phase differences become significant and
should be restricted to capturing reverberant or audience information. This
second pair of microphones should be between 12 and 24 dB down from the
primary pair or a phase monitor oscilloscope should be used. Using four
directional microphones, as two stereo pairs, on a single stand generally
degrades the sound so much as to render this technique unusable for stereo
ambient recordings.
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