Apple Impulse Response Utility - Manual (Page 5)

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The recorded sine sweep audio file cannot directly be used as an impulse response. The
recorded file contains all the echoes and reflections—in other words, the
response —of
the space, stretched out over the length of the sine sweep. This is very different to the
starter pistol approach, where the
response is contained at the beginning of the file in
an impulse .
When you use a sine sweep, Impulse Response Utility uses a process called
deconvolution to time align and level align all recorded reflections—that are present
over the entire recorded sine sweep—into the very beginning of the file. This results in
an impulse response that Space Designer can use to combine, or convolve, with your
audio signal. Impulse Response Utility can then generate an .sdir setting from the
impulse response.
Setting Up Your Impulse Response Recording System
Prior to using Impulse Response Utility to create an impulse response, you need to set
up your recording hardware—allowing playback and recording of the sine sweep that
Impulse Response Utility will generate.
Ideally, you will have:
 One speaker for each (speaker) location required by the chosen format, if you are
going to be generating sine wave sweeps. As examples: If you are recording a true
stereo impulse response, you will need two speakers; if you are recording a six
channel surround impulse response, you will want six speakers, and so on. If you are
not generating sine wave sweeps, you don’t need speakers to play them back (the
sound is generated by the starter pistol).
Note: In many cases, it is sufficient to record one speaker position (but all
microphone positions required by the chosen impulse response format), and create a
mono/omni discrete impulse response. This will result in a less CPU-intensive impulse
response in the required format. See “
Recording a Mono to Omni 5 Channel Impulse
Response ” on page 32.
 One or more microphones to record the resulting audio from each speaker (or your
gunshot) combined with its echo reflections. The number of microphones you will
need depends on the chosen impulse response format. As examples; if you are
recording a six channel surround impulse response, there are six microphone
positions, so ideally you would have six microphones; if you are recording a six
channel B-Format encoded impulse response—where only one microphone position
and four tracks are required—you would need fewer microphones, and so on. Please
see “
B-Format Surround Encoding ” on page 28 for more information.
 An audio interface that offers enough outputs to send a broadband audio sine
sweep into each speaker (if using sine sweeps), and enough inputs to record the
resulting audio from each position.