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Chapter 4: The Synthesis of Sound by ComputerSection 4.8: Granular Synthesis
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When we discussed additive
synthesis, we learned that complex sounds can be created by adding together
a number of simpler ones, usually sets of sine waves. Granular synthesis
uses a similar idea, except that instead of a set of sine waves whose
frequencies and amplitudes change over time, we use many thousands of
very short (usually less than 100 milliseconds) overlapping sound
bursts or grains. The waveforms of these grains are often
sinusoidal, although any waveform can be used. (One alternative to sinusoidal
waveforms is to use grains of sampled sounds, either pre-recorded or captured
live.) By manipulating the temporal placement of large numbers of grains
and their frequencies, amplitude envelopes, and waveshapes, very complex
and time-variant sounds can be created. |
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This applet lets you granulate a signal and alter some of the typical parameters of granular synthesis, a popular synthesis technique. |
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Figure 4.20 A grain is
created by taking a waveform, in this case a sine wave, and multiplying
it by an amplitude envelope. Clouds of SoundGranular synthesis is often used to create what can be thought of as "sound clouds"shifting regions of sound energy that seem to move around a sonic space. A number of composers, like Iannis Xenakis and Barry Truax, thought of granular synthesis as a way of shaping large masses of sound by using granulation techniques. These two composers are both considered pioneers of this technique (Truax wrote some of the first special-purpose software for granular synthesis). Sometimes, cloud terminology is even used to talk about ways of arranging grains into different sorts of configurations. Figure 4.21 Visualization
of a granular synthesis "score." Each dot represents a grain
at a particular frequency and moment in time. An image such as this one
can give us a good idea of how this score might sound, even though there
is some important information left out (such as the grain amplitudes,
waveforms, amplitude envelopes, and so on). |
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This is an excerpt of a composition by computer music composer and researcher Mara Helmuth titled "Implements of Actuation." The sounds of an electric mbira and bicycle wheels are transformed via granular synthesis. There are a great many commercial and public domain applications to do granular synthesis because it is relatively easy to implement and the sounds can be very interesting and attractive. |
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