On 2013-05-09, Justin Bennett wrote:
You can always record an omni along with your MS mic and get
horizontal B-format!
only, of course, if you are using 2x figure-of-8 mics, or a double MS
set up.
Theoretically it works with a pair of cardioids (XY; call them a and b),
the Blumlein pair (c and d) you're describing, or conventional M/S with
a cardioid and a fig-8 (M and S), and a number of intermediate pickup
patterns and microphone axes. That's because as long as your signal set
spans WXY, you can matrix from any combination to any other. So, modulo
scaling and sign convention, I believe you get W as-is, then
X=a+b-2W=c+d=M-W, and Y=a-b=c-d=S. The third extra channel doesn't need
to be W either, as long as it's not a linear combination of the others.
In practice your mileage may vary, because of imperfect matching between
the mics, failure of full coincidence, variance of the mics from an
ideal first order response which breaks the cancellation in the matrix
and leaks in higher order harmonics, and the fact that the farther you
go from WXY, the more illposed the matrix becomes, so that noise
amplification differs between the setups (think two subcardioids facing
just a few degrees off front center).
--
Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front
+358-50-5756111, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2
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