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Chapter 10 Convolution Reverb: Space Designer 137
Creating Impulse Responses
This section discusses briefly the different methods for creating your own Impulse
Response files for use with Space Designer.
About Impulse Responses
Impulse Responses are recordings (stored as AIFF, SDII or WAV files) made in acoustic
spaces. To create an impulse response the sound of a starter pistol, digital spike or sine
sweep is recorded inside the desired room together with the resulting reflections.
Starter Pistols
Starter pistol shots are quite loud allowing a good signal to noise ratio to be recorded.
However, a perfect, undistorted recording of a starter pistol shot is difficult to produce.
In addition starter pistol shots contain very little high or bass frequency information.
Digital Spikes
A digital spike contains a wide frequency spectrum. You can create a spike by using the
Pencil tool in Logic’s Sample Edit window to draw a single sample in a silent sound file
(a recording of silence). The catch with this method is that, although fast, the output
level is often too low to be usable. You can, however, boost the signal in Logic.
Sweeps
The downside with starter pistols or digital spikes is that they release their (high level)
energy in a very short time period. As an alternative, you can playback, and record a
broadband audio sweep with optimal recording levels. For this a sine sweep covering
the whole audible frequency range could be used.
The recording of a sine sweep that is played back in an acoustic environment is known
as a sine sweep response, rather than an impulse response.
By means of a deconvolution process the sine sweep is removed from the sine sweep
response recording, leaving you with an impulse response file that can be loaded into
Space Designer. This method of creating impulse responses often results in a superior
reverb sound quality.