Make new sound out of an old one. Granular synthesis cuts a source into grains a few milliseconds to half a second long, starts them many times a second from a point that moves through the source, and adds them up. The result is a texture, a drone, a frozen chord, or the source itself smeared and repitched, depending on four settings.
Grains
Grain length sets how much of the source each grain carries. Under 20 ms the grains are too short to carry pitch of their own and the output buzzes at the grain rate; around 80 ms they carry a recognisable fragment; at 300 ms and more they are short samples. Density is how many grains start per second. When it exceeds the grain rate the grains overlap and the output turns continuous; the level is scaled by the overlap so a dense setting does not get louder.
Position, scan and spray
Start is where in the source the first grains read, as a share of the stretch in memory. Scan moves that read position: 1 follows the source at its own speed, 0.25 stretches it four times, 0 freezes it, and negative values run it backwards. Spray offsets each grain at random around the read position, as a share of the source. A little spray smooths a frozen sound; a lot turns any source into a cloud of its own moments.
Pitch and spread
Pitch plays every grain at a rate, in semitones, without changing how fast the read position moves. Stereo spread places each grain at a random pan, and because the grains are many the result is a wide, moving field rather than a ping-pong.
Output
Length is the output’s duration, independent of the source. The preview renders the first 8 seconds to WAV and plays them; the download renders the whole length in the chosen format. The grain sequence is fixed, so the two are the same sound.