The Kyma Language for Sound Design, Version 4.5

Reverberation
Select the GenericSource, and play it by itself. This is a recording of Pete Johnston singing his own favorite
canon into pete’s dual delay. § Now compare it to the chorused version by selecting and playing
chorusing using random. In the virtual control surface, type in a value of 0 for the !Delay, and hit Enter
or Return. This is the source with no chorusing. Then type in a 1 and hit Enter or Return. This is the
maximum chorusing.
How is it that we can almost always tell the difference between one person singing and several people
singing in unison? One factor is that different sound sources are different distances from your ear, so
there should be slightly different delays on each performer. Another is that the performers may be
slightly out of tune with each other. Both of these effects can be modeled using a DelayWithFeedback
with a variable delay time.
Look at the parameters of 10-25 ms. The Delay is set to 25 ms and the DelayScale (the proportion of
Delay that is actually used) is
0.7 + ( randLFO1 L abs * !Delay * 0.3)
In other words, the maximum delay time of 25 ms is multiplied by a number that varies between 1 (0.7 +
0.3) and 0.4 (0.7 - 0.3), depending on the value of !Delay and of the low frequency oscillator.
The low frequency oscillator is a sine wave oscillator with a subaudio, random frequency. Take a look at
randLFO1, in particular, its Frequency parameter:
0.37 hz + 1 s random hz
This looks a little confusing because there is a time value in a frequency field, but the time just refers to
how often a new random number should be generated. The expression
1 s random hz
generates a random frequency between -1 hz and 1 hz and changes to a new random frequency once per
second. When added to 0.37 hz, it gives the LFO a frequency range of -0.63 to 1.37 hz. A negative frequency
tells the Oscillator to read through its wavetable backwards. In the sine wave case, a negative
frequency sounds the same but is 180 degrees out of phase from the same frequency without the minus
sign.
Take a look at some of the output of randLFO1 by selecting it, choosing Full waveform from the Info
menu, and asking it to plot 10 seconds of the output. (Because the Oscillator’s duration is on, you must
specify the amount of time to plot). This signal is controlling the delay, so the delay times will vary
smoothly above and below some fixed delay but at a random rate.
When a sound wave propagates within an enclosed space, it takes some amount of time to get from the
sound source out to the edges of the enclosure where it runs into a wall; some of the energy is absorbed
by the wall, and some of it gets reflected back into the room, taking some additional time to get to your
ear.
§ Besides being the Technical Director and Kyma guru at Tape Gallery in London, Pete does a pretty good imitation
of Freddie Mercury in this recording (though he says he can do even better when he is not out of practice).
109