The basic premise behind granular synthesis is that a sound can be broken down into tiny particles, or grains. In many respects, granular synthesis is similar to wavetable synthesis, but it works on a much finer scale. This method is ideal for creating constantly evolving sounds and truly unique tones.
Alchemy extracts sampled grains—2- to 230-milliseconds long—which can be manipulated, reorganized, or combined with grains from other sounds to create new timbres. The effects that result from this technique depend on factors such as the duration and amplitude envelope of each grain, the degree of overlap or separation from one grain to the next, and the pitch and pan position of each piece of sound.
If each new grain is extracted from slightly further into the sample than its predecessor, playback of the resulting stream of grains in their original sequence, at the original speed, essentially puts the pieces of sound back together to closely resemble the source audio material. If you play back the stream of grains at a slower speed, separation (a small gap) occurs between grains. If you play back the stream of grains at a faster rate, each grain overlaps with the next one.
A number of interesting manipulations are possible using this synthesis method.
Time-stretching. Grains can be sent out at a faster or slower rate than their counterparts in the original sample, allowing faster or slower playback—without the changes to pitch that occur with traditional sample playback. You can even “freeze” a sample at a certain position by extracting multiple grains from a single point. On this latter point, you could repeat a drum hit “grain” multiple times in a time-stretched loop to create a different drum pattern, for example.
Pitch-shifting. Modifications to the pitch of each grain allow you to vary the pitch of a sample without affecting its timing. By modulating the pitch or pan position of each grain, you can also create spatial and “blurring” effects.
You can also scramble the order in which grains are played back to produce effects ranging from mild fuzziness to extreme mangling.