Convolution can be used musically for cross-filtering of sounds and for simulating reverb. The process is the same, no matter your musical intention. Different musical effects can be obtained by using impulse files of various lengths and amplitude shapes.
Convolution in SoundHack
SoundHack implements convolution as a file process, the same as its other processing (or “Hack”) commands. In the case of convolution, you start with an source file, choose convolution from the Hack menu, choose an impulse file, set final options, and process. Even though convolution doesn’t care which file is the input and which is the impulse, I will generally think in terms of the input file as being the source file that will have the impulse convolved with it.
- Launch SoundHack
- Open a soundfile as your input file
- Choose Convolution (cmd-C) from the Hack menu
- Choose Pick Impulse from the Convolution dialog window
- Open the soundfile to use as your impulse file
- Set you processing options in the Convolution dialog window
- Select 42 dB gain, as a general rule (convolution almost always leads to greatly reduced amplitudes)
- I do not select any of the four bottom options (ring modulate, moving, brighten, normalize).
- Click on the Process button, and choose a filename for the output file
You will then want to open the output file in a stereo audio editor and normalize it. I have had problems with the SoundHack normalize function, so I tend to normalize as a separate step in Audition.
One thing to remember: if you want to John Malkovich a file (convolve it with itself), you need to create a duplicate of the soundfile. SoundHack won’t let you use the same file as the input and impulse.