Apple Impulse Response Utility - Manual (Page 4)

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Deconvolution is the process used to create impulse responses from (recorded)
broadband audio sine sweeps. The following section covers deconvolution and its role
in the impulse response creation process. Further sections discuss the hardware
necessary for impulse response recording, and use of Impulse Response Utility to make
your own Space Designer Impulse Response (.sdir) files.
Deconvolution and Impulse Response Utility
Space Designer combines, or convolves , an impulse response of an acoustic space with
an audio signal. The end result is that your audio is placed “inside” the acoustic space,
represented by that impulse response. Think of an impulse response as the total echoes
(reflections) in a given physical space, following an initial signal spike. The impulse
response file is simply an audio file recording made in a space that contains these echoes.
Making an Impulse Response Recording
There are two practical methods used for impulse response recording.
Using a Transient Recording
The first method involves the recording of an impulse in a space, using a device such as
a starter pistol. The gunshot is the impulse, and the audio file you record captures both
the impulse (gunshot) and the room response.
The advantage of this method is that the recorded audio file can be used in
Space Designer without any further processing. You can simply use Impulse Response
Utility to record your starter pistol impulses, and then combine them into a
Space Designer Impulse Response (.sdir) file (and Space Designer setting file).
The disadvantage of this method is that it’s extremely difficult to make a perfect,
undistorted recording of a starter pistol shot. This is due to the extremely loud nature
of the initial transient of the shot. A further issue is that starter pistol shots contain very
little high or bass frequency information—which, in turn, limits the usable frequency
range of the convolved reverb.
Using a Broadband Sine Sweep
The second (and preferred) method for creating impulse responses involves playing a
broadband audio sine sweep into a space, and recording the sweep (and space) at
optimal recording levels. A sine sweep that covers the entire audible frequency range is
used, resulting in a broad-range, and often higher quality, impulse response.