<<If an AB pair is used, converting to mono in post-production is
simply a matter of using only one of the mic signals (unless they're
very widely spaced apart and/or very close to the sound source, the
two mics should sound pretty much identical with only time
differences between them). That's not going to be much help if the
stereo signal is being converted to mono during playback (in which
case you have to be careful of comb filtering when placing the mics),
but it does give the post-production people something useful to work
with.>>
If the spacing of the AB pair is great enough that a given source is
nonexistant in one or the other channels or sounds vastly different,
it doesn't really constitute a true stereo signal & must be handled
as a multichannel session, i.e. dual mono. Decca Tree was developed
in order to fill in information which was largely absent when widely
spacing an omni pair. AB omni spacing, i.e. a meter or less, doesn't
provide a great deal of stereo width, & wider spacing doesn't provide
a coherent center, so a third mic was added to the center, allowing
for the dramatic width as well as solid center experienced with the
Decca approach.
Scott Fraser
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