Grain density spans texture from discrete rhythmic events to continuous tone

Grain density — the number of grains emitted per second — is one of the most important parameters of granular synthesis, equivalently expressed as the interval between grain triggers (its inverse: longer interval means lower density). In synchronous granular synthesis it corresponds to a regular emission frequency, and a single control spans the whole continuum: at ~2 grains/sec a grain sounds every half second (a repeating beep); ~0.1–20 grains/sec generate metrical rhythms (varying density over time yields precise accelerandi/rallentandi); several hundred to several thousand grains/sec fuse long grains into a continuous tone with a strong fundamental and, depending on grain envelope and duration, sidebands. Together with grain duration, density sets average overlap (overlap = density × duration): low density with short grains gives a sparse, pointillistic scatter; high density with longer grains gives a thick, continuous cloud. Density is independent of grain pitch, so a cloud can be thickened or thinned at a fixed pitch — the cross-cutting of parameters that gives granular synthesis its expressive flexibility.

Examples

2 grains/sec = repeating beep at half-second intervals; ~10 grains/sec = metric pulse; 2000 grains/sec = lush near-continuous pad. A granular cloud from a sampled cello: thinly veiled at 200 grains/sec, reverberant at 2000, with pitch fixed by each grain’s internal frequency. Trigger grains every 20 ms for a dense cloud; widen to 200 ms for a sparse stutter.

Assessment

Describe what happens to a synchronous grain stream as density rises from 2 to 2000 grains/sec, and at roughly what range it shifts from metric rhythm to continuous tone. Explain why density and pitch are independent, and why density and trigger interval are two views of the same control.