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Granular synthesis is a basic sound synthesis method that operates on the microsound time scale. It is often based on the same principles as sampling but often includes analog technology. The samples are not used directly however, they are split in small pieces of around 1 to 50 ms (milliseconds) in length, or the synthesized sounds are very short. These small pieces are called grains. Multiple grains may be layered on top of each other all playing at different speed, phase and volume.
The result is no single tone, but a soundscape, often a cloud, that is subject to manipulation in a way unlike any natural sound and also unlike the sounds produced by most other synthesis techniques. By varying the waveform, envelope, duration, spatial position, and density of the grains many different sounds can be produced.
The result is usable as music, sound effects or as raw material for further processing by other synthesis or DSP effects. The range of effects that can be produced include amplitude modulation, time stretching, stereo or multichannel scattering, random reordering, disintegration and morphing.
Dennis Gabor researched how human beings communicate and hear. The result of his investigations was the theory of granular synthesis, although Greek composer Iannis Xenakis claimed that he was actually the first inventor of this synthesis technique (Xenakis, Formalized Music, preface xiii).
Curtis Roads is often credited as the first person to implement a digital granular synthesis engine. Canadian composer Barry Truax was one of first to implement real-time versions of this synthesis technique.