The Kyma Language for Sound Design, Version 4.5

Compression, Expansion
Compression
Expansion
Other Effects
The Sounds in this file are examples of using the DynamicRangeController (DRC) module to compress or
expand the dynamic range of another Sound. The DRC performs a time-varying attenuation on its Input
based upon the amplitude envelope of the Sound used as its side chain input.
The idea of compression is to take the full range of amplitudes and compress them into a narrower range
by attenuating the larger amplitudes, and then optionally scaling all of the amplitudes up so that the low
amplitude parts of the signal become much louder relative to the maximum.
By way of analogy, if you were listening to music through speakers and kept your hand on the volume
knob of the amplifier, and turned it down whenever it got loud and turned it back up again whenever the
music got soft, you would be acting as a compressor. Of course since there would be some amount of delay
between when you heard the music get loud and when your reflexes actually managed to turn down
the volume, this would work better if you could listen to the music directly over headphones and could
delay the output through the speakers by some small amount. For the same reason, there is a delay parameter
on the DRC, so that there is time for the DRC to attenuate sudden changes in the amplitude
envelope.
You can use a compressor to prevent an input from ever getting too loud; for an example select orig,
limiter (Info-Full waveform), and choose Full waveform from the Info menu. Another application of
compressors is removing unwanted amplitude variations, caused, for example, by performers moving
around with respect to the microphone (plot the full waveform of orig, smoothed out (Info-Full waveform)
as an example).
There is also a characteristic timbre to compressed sounds, and it can make percussive and plucked string
sounds seem, psychoacoustically, louder or “punchier” by reducing the difference between their sharp
attacks and quick decays — in effect stretching out the decay time so that the sound stays louder for a
longer period of time.
For an explanation of the DRC parameters, find the DynamicRangeController in the Dynamics category
of the prototypes. Select it, and then choose Describe Sound from the Info menu. Leave that window
open, and play the Sound called Compressor w/hot controls in the compression, expansion Sound
file window. Then you can experiment with different parameter settings.
Expansion (not too surprisingly) is like the opposite of compression; it takes amplitudes that might have
been very close together in the original amplitude envelope, and spreads them further apart in the amplitude
envelope of the output. For example, you might want to take all amplitudes below some noise
floor and specify that they should be mapped to zero amplitude (or close to zero amplitude), creating a
kind of “noise gate” to remove unwanted background noise when it is softer than the desired signal. Examine
the Sound called noise gate to see an example of this.
Experiment with the Sound called Expander w/hot controls to hear the effect of different parameter settings.
By using different Sounds at the side chain and the input, you can create other effects like ducking, gating,
or de-essing.
Take a look at the Sound called Ducking. It is set up as a compressor with a speaking voice as the side
chain and a violin sample as the Input. Whenever the speaking voice is triggered, the violin sample
“ducks” behind it into the background.
use voice to gate another sound is similar except that it is set to expand instead of compress, so when the
voice is triggered, it opens the gate on the Noise input, and when the voice is silent, the gate is closed.
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