Apple Impulse Response Utility - Manual (Page 28)

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This scenario requires neither speakers or microphones. You can simply connect the
output from your audio interface to the input of your hardware device, and play the
sine sweep through it. Connect the output of your hardware device to the input of
your audio interface, and record it back into Impulse Response Utility. You can use this
method to make impulse responses from classic hardware reverbs, multi-effects units,
equalizers, and so on.
You should take care when making impulse responses from hardware effects devices
that include modulation effects. Modulations such as phasing, choruses, and so on,
interfere with the sine sweep itself, which makes deconvolution difficult or impossible.
This is also true for some reverbs, such as classic Lexicon hardware reverb devices, in
which the reverb tails are modulated. In these cases, you may be better off sending a
recorded impulse (such as a recorded spike or gunshot) through the hardware effects
device, instead of a sine sweep.
B-Format Surround Encoding
B-Format is a special way of encoding spatial information. It represents space using four
audio streams: one to capture the sound pressure (W), and three to capture the X
(front-to-back), Y (left-to-right), and Z (top-to-bottom) room co-ordinates. The following
illustration shows you how these four audio streams interact with each other, to create
a three-dimensional spatial image.
Height
Z
Front
X
Right
Y
Z
Y
Left
X
Rear
W