Overview
This article describes a flexible architecture for Real-Time Granular Synthesis that accommodates a
number of Granular Synthesis variants including Tapped Delay Line, Stored Sample and Synthetic Grain
Granular Synthesis in both Pitch Synchronous and Asynchronous forms. Three efficient algorithms for
generating grain envelopes are reviewed and two methods for generating stochastic grain onset times are
discussed. Readers are advised to consult the literature for further information on the theory and
applications of Granular Synthesis.1, 2, 3,4,5
Background
Granular Synthesis or Granulation is a flexible method for creating animated sonic textures. Sounds
produced by granular synthesis have an organic quality sometimes reminiscent of sounds heard in nature:
the sound of a babbling brook, or leaves rustling in a tree. Forms of granular processing involving sampled
sound may be used to create time stretching, time freezing, time smearing, pitch shifting and pitch smearing
effects. Perceptual continua for granular sounds include gritty / smooth and dense / sparse. The metaphor of
sonic clouds has been used to describe sounds generated using Granular Synthesis. By varying synthesis
parameters over time, gestures evocative of accumulation / dispersal, and condensation / evaporation may
be created.
The output of a Granular Synthesizer or Granulator is a mixture of many individual grains of sound. The
sonic quality of a granular texture is a result of the distribution of grains in time and of the parameters
selected for the synthesis of each grain. Typically, grains are quite short in duration and are often
distributed densely in time so that the resultant sound is perceived as a fused texture. Algorithmic means
are usually employed to determine when grains occur in time and to select their synthesis parameters,
which often include duration, amplitude, panning, pitch, and envelope shape. A Stochastic Granular
Synthesizer uses random number generators to determine grain onset times and synthesis parameters.
Usually, the probability functions of these random number generators constitute the parameters of the
Granulator as a whole and are often varied over time.
Granular Synthesis differs from many other audio synthesis techniques in that it straddles the boundary
between algorithmic event scheduling and polyphonic event synthesis. Conventional synthesis techniques
are typically employed in the creation of individual musical ‘notes’, whereas Granular Synthesis may
employ thousands or millions of relatively simple grains to articulate a single sonic gesture. One
implementation of Granular Synthesis using MIDI synthesizers was described as Rapid Event
Deployment highlighting the central role of event scheduling in Granular Synthesis
