<<C
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A--------x--------B
testing using spaces instead of tabs. the last ascii diagram got mangled
hope this one works better>>
Still mangled. Let me try an alternative Decca description: Stretch
both arms straight out to your left & right. Grab an omni mic in each
hand & aim outward at a 30 to 60 degree angle. Now imagine a center
mic mounted anywhere from mid-arm to full arm's length directly out
in front of your neck. That's a basic Decca arrangement & it is
placed close to & over the orchestra, with the mics aimed down. The
set up can scale larger or smaller depending on the size of the
soundstage it is intended to pick up. The arm's length model would
work well for the average chamber ensemble, a somewhat larger size
works for a symphonic orchestra, & smaller is appropriate for a
string quartet. As for ambient field recording, I personally don't
see the application working very well. The Decca stereo field is a
result of arrival time & amplitude differences between the 3 capsules
& is governed largely by the proximity of each element in the stereo
field to any given mic in the array. In other words, the first
violins are clearly heard primarily left because they may be as much
as 50% closer to the left mic than the others. On the other hand, a
bird 50 feet or more horizontally in the distance will basically be
picked up equally well by all three mics, because it is not within
the general depth of field perceived by the offset arrangement &
overhead placement of the Decca tree. If you can get up & over an
active sound environment with a Decca arrangement, it will result in
a deep, three dimensional sound field. Otherwise, at a distance, a
standard XY, MS, ORTF or AB stereo approach will provide a more
coherent stereo image.
Scott Fraser
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