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Spaced microphone techniques were the first methods employed to relate
a stereo image to the listener. Bell Labs did a lot of work on these methods.
They experimented with two and three spaced microphones, adding the third
microphone to "fill in the center image". This method has the microphones
facing forward along a line perpendicular to the sound source. The polar
pattern , spacing and distance from the sound source are all variables that
need to be considered using this technique. Unlike the other methods
described here, this method creates a stereo image as a result of both time
and amplitude differences between channels.
Two significant problems can arise using this method.
They are :
1) Vague center imaging. Keeping the microphone spacing to a minimum will
alleviate this problem. A spacing of 2 to 10 feet is best depending on the
distance from the sound source. For nature recording keep the mics to about 24".
and
2) low-frequency comb-filter effects on sounds sourced to the extremes of the
soundstage. A phase monitor oscilloscope or laptop with appropriate software
should be used with these methods to assist in microphone placement.
Another concern, to some, is erratic mono compatibility.
The main advantage of this technique is that Omnidirectional microphones
exhibit little or no tonal shift and have a very open sound. This makes them ideal
for recording nature sounds or music when tonal accuracy is a must.
Another significant advantage of Omnidirectional microphones is that they are
relatively immune to windnoise.
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