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github-actions[bot] edited this page May 2, 2026 · 1 revision

Generative Music

Flow has several primitives for algorithmic and probabilistic music: Euclidean rhythms, weighted random choice, seeded randomness, sequence mutation (vary), and polyrhythm construction.

Euclidean Rhythms

Distribute k hits evenly across n steps using the Bjorklund algorithm:

use "@std"

Sequence e38 = (euclidean 3 8 C4)
(print (str e38))    Note: X..X..X. style pattern

Sequence e58 = (euclidean 5 8 E4)
(print (str e58))

Signature: (euclidean Int hits, Int steps, Note pitch) -> Sequence

Common Euclidean patterns map to global rhythmic traditions:

hits / steps Feel
3/8 Cuban tresillo
5/8 West African bell pattern
3/4 Simple triplet
7/16 Afro-Cuban bembé

Random Choice in Note Streams

Pick a note at random from a set. This is syntax, not a function — it works only inside | ... | note streams.

Uniform Random

(? ...) picks one of the listed notes with equal probability on each evaluation:

use "@std"

timesig 4/4 {
    Sequence random = | (? C4 E4 G4) (? C4 E4 G4) (? C4 E4 G4) (? C4 E4 G4) |
}

Weighted Random

Append :weight to bias the selection:

timesig 4/4 {
    Sequence weighted = | (? C4:50 E4:30 G4:20) (? C4:50 E4:30 G4:20) _ _ |
}

Weights are relative, not percentages. :50 :30 :20 is equivalent to :5 :3 :2.

Including Rests

Rests (_) can be options too:

timesig 4/4 {
    Sequence sparse = | (? C4 _) (? E4 _) (? G4 _) (? C4 _) |
}

Seeded Random

(?? ...) is a second, separately seeded RNG. It produces reproducible output once a seed is set.

use "@std"

(??set 42)
timesig 4/4 {
    Sequence seeded = | (?? C4 E4 G4) (?? D4 F4 A4) (?? E4 G4 B4) (?? C4 E4 G4) |
}
Function Effect
(??set N) Set the seeded RNG state to N
(??reset) Reset the seeded RNG to its initial state
(??) Get a random Float from the seeded stream
(?) Get a random Float from the unseeded stream

Sequence Mutation (vary)

vary applies random mutations to a sequence. You can choose what to mutate and whether to constrain output to a key.

use "@std"

Sequence s = | C4 D4 E4 F4 G4 |

Note: basic mutation (random type, 30% chance per note)
Sequence v1 = s -> vary(0.3)

Note: specific mutation type
Sequence v2 = (vary s 0.5 "pitch")
Sequence v3 = (vary s 0.5 "rhythm")
Sequence v4 = (vary s 0.5 "rest")
Sequence v5 = (vary s 0.5 "velocity")

Note: seeded (reproducible)
Sequence v6 = (vary s 0.5 42)

Note: seeded + type
Sequence v7 = (vary s 0.5 "pitch" 42)

Note: diatonic — constrain pitch mutations to a scale
Sequence v8 = (vary s 0.5 "pitch" "Cmajor")
Sequence v9 = (vary s 0.5 "pitch" "Cmajor" 42)

Overloads

Signature Description
(Sequence, Double) -> Sequence Random mutation type
(Sequence, Double, String) -> Sequence Specific type
(Sequence, Double, Int) -> Sequence Seeded random type
(Sequence, Double, String, Int) -> Sequence Seeded, specific type
(Sequence, Double, String, String) -> Sequence Diatonic (type, key)
(Sequence, Double, String, String, Int) -> Sequence Diatonic, seeded

Mutation types

Type Effect
"pitch" Shift pitch up/down, optionally snapping to key
"rhythm" Randomize note durations
"rest" Replace note with rest
"velocity" Randomize velocity

Polyrhythms

Overlay two sequences with different time signatures. polyrhythm figures out the cycle length (LCM of time signatures) and returns a mixed buffer:

use "@std"
use "@audio"

tempo 120 {
    timesig 3/4 {
        Sequence waltz = | A3 E4 E4 |
        timesig 4/4 {
            Sequence quarters = | C4 C4 C4 C4 |
            Buffer poly = (polyrhythm waltz quarters)
            (exportWav poly "polyrhythm.wav")
        }
    }
}

Signatures

Signature Description
(polyrhythm Sequence, Sequence) -> Buffer Auto-align via LCM of time signatures
(polyrhythm Sequence, Sequence, Int) -> Buffer Explicit beat count override

Combining Generative Techniques

Generative primitives compose cleanly:

use "@std"
use "@audio"

tempo 120 {
    timesig 4/4 {
        key Cmajor {
            Note: a Euclidean hi-hat
            Sequence hat = (euclidean 5 8 C5)

            Note: a seeded melodic line
            (??set 7)
            Sequence lead = | (?? C4 E4 G4 B4) (?? D4 F4 A4) (?? E4 G4 B4) (?? F4 A4 C5) |

            Note: diatonic mutation on the lead
            Sequence varied = (vary lead 0.3 "pitch" "Cmajor" 7)

            section groove {
                Sequence a = hat
                Sequence b = varied
            }
            Song song = [groove*4]
            Buffer buf = (renderSong song "piano")
            (exportWav buf "generative.wav")
        }
    }
}

See Also

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