Granular synthesis provides us with a method of changing pitch and time independently of each other. It works on the principle that any sound can be thought of as a discrete particles, or segments of time. These discrete particles are referred to as grains. The process is analogous to color printing or viewing images on a TV or computer monitor. Images are comprised of discrete pixels, usually comprised of limited colors, that are combined to create continuous color fluctuation in what appears to be a single image. For sound, grain durations typically fall between 1 ms to 100 ms.
- Playback speed
- Index location (location in source soundfile used to read audio)
- (maximum) amplitude
- Grain envelope (shape of the amplitude envelope)
Grain parameters do not vary within a single grain. To create a sound that changes over time, you change the initial parameters to subsequent grains.
parameters of grain combinations
Parameters of grain combinations affect the use of two or more grains together or in sequence.
- Frequency of grains (how many grains per second)
- Density of grains (the number of grains happening at one time, can be thought of as the vertical analog to the horizontal frequency of grains)
- Number of grain streams (can be related to density), sometimes referred to as the number of overlaps.
windows (grain envelopes)
- A window is a short-time amplitude envelope. The total length of the window matches the grain duration.
- The window shape can be chosen to emphasize legato amplitude connections between grains, amplitude discontinuity between grains, or anywhere in between.
- Although Cecilia defaults to a sine window for the Filter Warper, better results will usually be had with the Hamming window (more like a bell curve).
overlaps and streams
- A stream is the individual series of grains occurring one after another.
- Multiple streams involve overlapping envelopes.
- Overlapping envelopes generally produce a smoother amplitude output.
high-level (macro) organization
The number of parameters per grain to control, and the number of grains to generate per second, require some type of macro control.
- Pitch-Synchronous organization analyzes the sound file ahead of time to set parameters so that a specified pitch will result. The parameter settings of individual grain parameters are linked. Kontakt tone machine uses pitch-synchronous organization. At this level, we do not have any tools to produce pitch-synchronous organization.
- Asynchronous organization means that all grain parameters are specified independently of each other. Control functions are usually specified to change parameters over time. Asynchronous means that any changes to one grain have no effect on any other grain.
- Quasi-synchronous organization indicates that some, but not all, parameters are linked. It is the most common organization offered in the programs we use (Cecilia). Most often, grain duration determines the frequency of grains, as grains are created in succession. (This organization leads to a type of AM synthesis, or tremolo.)