(compMus2) Granular Synthesis Intro


Any sound can be thought of as containing discrete particles, or segments of sound. To make a comparison, granular synthesis is similar to pointallism in visual art. In sound synthesis, grains typically last from 1 ms to 100 ms, although longer grains are possible with some software. Each grain is shaped by an amplitude envelope (window). Within each grain, sound parameters are fixed. Change occurs on a grain-by-grain basis.

Grain parameters include pitch (playback ratio), panning, grain duration, envelope, and location in sound file. In addition, the frequency of grains (how many grains occur per second) and how many streams (or layers) of granular activity can also be controlled.

High-Level Organization

Since granular synthesis generates so many grains per second, some form of macro control is needed. Synchronous (Pitch-Synchronous) control analyzes sound ahead of time, and makes modifications to parameters in order to force pitch onto the output of the granular synthesis operation. Synchronous control means that parameter values are linked; if one parameter changes, others must change in specific ways.

Asynchronous control treats all parameters independently. The resulting granular output is often compared to clouds or a jet nozzle on a water hose.

Synchronous and asynchronous control represent two extremes of control. Much granular synthesis is of the Quasi-Synchronous variety. Quasi-synchronous control is generally favored for time compression and expansion independent of pitch change, and pitch change independent of time change. Changes occur to the grain length, but grains generally follow at regular intervals. The output result can be thought of as similar to AM synthesis, but with overlapping streams and changing grain lengths the modulation effect can be made more or less prominent.


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