poisson-cloud

poisson-cloud scatters a decaying swarm of grains behind every note you play.

One key press becomes a small stochastic texture: grain onsets follow a Poisson process at density grains per second, thinning out to nothing across duration, and each grain lands near your note (Gaussian, sigma semitones wide) with a velocity that fades as the cloud dies plus its own noise (vel-sigma). This is composition by distribution law in the manner of Xenakis’s Pithoprakta and Achorripsis: not which notes, but how many per second, spread how far. You play the center of mass; the cloud does the rest.

The played note passes through unchanged and releases when you release it. Every grain carries its own note-off (a grain lasts until the next arrival, at most 120ms), so note-ons and note-offs always balance and nothing hangs; a grain that wanders off the keyboard is dropped whole. The cloud is seeded: the same seed and the same playing spray the same grains, forever; see Seeds.

Parameters

duration= takes a duration string like "250ms" or "1.5s", or beats= against the tempo, never both; see Time and tempo.

Parameter	Type	Default	Range
seed	integer	required	any unsigned 64-bit value
density	number	8.0	0.1..=50.0 grains per second
duration	duration string	"2s"	positive, "250ms" or "1.5s" form
beats	number	none (instead of duration)	finite, greater than 0
sigma	number	7.0	0..=24 semitones
vel-sigma	number	10.0	0..=40 velocity steps
max	integer	16	1..=24 grains per note

Example

miditool.kdl

input "Roland"
output virtual="miditool Out"

poisson-cloud seed=17 density=12 duration="1.5s" sigma=9.0 vel-sigma=12.0 max=20

Play single staccato notes and each one bursts into a second and a half of scattered aftermath. This is the clouds scene from examples/clouds.kdl, which follows it with velocity-dice to reroll every grain’s dynamics.

Try this

Set sigma=0.0 and the whole cloud stays on the played key: a granular tremolo dying away.

tempo 84

poisson-cloud seed=5 density=4 beats=4 sigma=0.0 vel-sigma=20.0 max=24

Then widen it back out: sigma=14.0 at this low density is sparse pointillism, stray notes flickering one at a time around whatever you touched.