Rhythm and groove

Rhythm in claudius has three layers: where notes sit (patterns and step strings), how hard they are played (velocity), and how the grid is bent when the song renders (swing and humanize). This page gives the exact behaviour of each and the idioms that come out of them.

The grid

Pattern time is continuous: a cycle is one bar, and mini-notation divides it however you like. Common subdivisions:

Drum lanes (drum()) are a step grid with 16 steps per bar by default, or any resolution from 1 to 96. When a lane prints as a script, it uses 16 steps if every hit sits on a sixteenth, then 32, then 48.

Velocity

Velocity drives level and tone the way the instrument does. Synthesized drums and audio files scale level by velocity to the power 1.6 (0.5 is about 10 dB below 1.0); the sampled kits switch velocity layers (the 909 has eleven) as well; synth presets open their filters. The track as a whole is then levelled to its role’s target, so velocity shapes the groove, not the track’s loudness.

A sixteenth hat with accents on the off-beat eighths and soft ghosts between:

blank("house");
tempo(124);
track("hats", s("hh*16").bank("tr909").gain("[0.35 0.2 0.8 0.2]*4"));

Swing

swing(amount) is sixteenth-note swing for the whole song:

• each off-beat sixteenth (the second of each pair inside an eighth note) moves to amount of the way through the eighth; 0.5 is straight, 0.66 is a triplet feel; the range is 0 to 0.8, and up to 0.501 is straight;
• only notes within 0.01 beats of a sixteenth grid position move, so eighth notes, triplets and notes nudged with .late() are untouched;
• it applies at render to every track: drum lanes, parts and pattern tracks alike.

The genres’ generated swing ranges are a good guide: house 0.50–0.56, deep house 0.53–0.58, lofi 0.56–0.63, trap 0.50–0.54, techno 0.50–0.52, drum and bass 0.50–0.51, future bass 0.50–0.53, synthwave straight.

Since swing is global, a part that should sit straight in a swung song has to avoid off-beat sixteenths (use eighths or triplets), and a part that should lag can use .late(0.01) to .late(0.03), which also takes it off the grid that swing moves.

Humanize

humanize(amount) adds random timing and velocity at render:

• timing: a normal distribution with a standard deviation of 4 ms × amount on drum roles, 2.4 ms × amount on others (synth tracks: 3 ms and 1.8 ms);
• velocity: ±5 % × amount (one standard deviation);
• seeded by the song and the track name, so every render is the same.

Generated songs use 0.25 in house, 0.35 in deep house, 0.6 in lofi, 0.15 in trap and 0.1 elsewhere. blank() keeps the genre’s value.

Idioms

Ghost notes are low-velocity hits between the main ones. In a step string, o; in a pattern, a quiet layer in a stack(), since a gain pattern applies by time and would turn down the backbeat too:

blank("lofi");
tempo(86); swing(0.6);
track("snare", stack([s("~ sd ~ sd").gain(0.9), s("~ ~ ~ [~ sd] ~ ~ [~ sd] ~").gain(0.3)]).bank("acoustic"));

Rolls are fast repeats inside one beat. Write the bar beat by beat, with the roll in the beat that has it:

blank("trap");
tempo(140);
track("hats", s("<[hh*2 hh*2 hh*2 hh*2] [hh*2 hh*2 hh*2 hh*6] [hh*2 hh*2 hh*2 hh*2] [hh*2 hh*4 hh*2 hh*8]>")
                .bank("tr808").gain("[0.9 0.6]*4"));

Bar 2 ends with a sixteenth-triplet roll (six in a beat), bar 4 with thirty-seconds. Generated trap hats get rolls from the drum grammar instead: random beats replaced by bursts of thirty-seconds or triplets with a rising or falling velocity ramp, most often on the last beat of a bar and rarely on the first.

Euclidean rhythms spread k hits over n steps as evenly as possible, which gives most of the world’s clave-like patterns: (3,8) is the tresillo (x..x..x.), (5,8) the cinquillo (x.xx.xx.), (5,16) and (7,16) are good percussion lines over a four-on-the-floor kick. A third number rotates the rhythm left by that many steps (see Euclidean rhythms).

blank("techno");
tempo(130);
track("kick", s("bd*4").bank("tr909"));
track("rim",  s("rim(5,16,2)").bank("tr909").gain(0.6).pan(0.3));
track("perc", s("cb(3,8,1)").gain(0.4).pan(-0.3));

Polymeter. There is no { } polymeter, but a fractional fast() runs a short figure across bar lines. A three-step figure on a sixteenth grid is three sixteenths long, so it repeats 16/3 times per bar:

blank("techno");
track("perc", s("rim ~ ~").fast(16.0 / 3.0).gain(0.5));   // lands one sixteenth earlier each bar

It restarts with every section, like every pattern.

Kick and bass together. A bass that plays exactly with the kick uses the kick’s rhythm as its structure. Keep the rhythm in a variable so the two cannot drift apart:

blank("trap");
tempo(140); key("C minor");
let kick = "x ~ ~ ~ ~ ~ ~ x ~ ~ x ~ ~ ~ ~ ~";
track("kick", s("bd").struct(kick).bank("tr808"));
track("808",  note("<c2!2 ab1!2 f1!2 g1!2>").struct(kick).s("808").legato(1.0));

Generated parts do the same with the kick_follow bass style, which plays on every kick of the main kick pattern.

Drum lanes in the arrangement

Drum lanes change with the sections they play in:

• each section plays the lane’s variant it asks for (main, sparse, alt, half …), or main when the lane does not have it; intros and outros ask for sparse;
• fills() replaces the last one or two beats of every 8-bar phrase on the snare (or clap) lane with a fill, and sometimes drops the kick for the last half beat;
• build() turns the snare (or clap) lane into a snare roll for the second half of the build and drops the kick for its last bar.

Form and sections has the exact rules. Pattern tracks are never rewritten; make fills with lastOf() and builds with a track that only plays in the build:

blank("house");
tempo(124);
track("drums", s("bd*4, [~ cp]*2, [~ hh]*4").bank("tr909").lastOf(8, |x| x.ply(2)));
track("roll",  s("<sd*2 sd*2 sd*4 sd*4 sd*8 sd*8 sd*16 sd*16>").bank("tr909")
                 .gain("<0.4 0.45 0.5 0.55 0.65 0.75 0.85 1>"));
form([sec("groove", 16, "drums"), sec("build", 8, "roll").gap(), sec("drop", 16, "drums").impact()]);

The generator’s grooves

Generated drum lanes come from each genre’s drum grammar: for every lane, a probability of a hit on each sixteenth step (1.0 always hits), a velocity range scaled by the metrical weight of the step, a chance of ghost notes, a chance of rolls, and a chance that the last bar of the 4-bar pattern varies. Some lanes use a euclidean rhythm instead (house percussion is a rotated (5,16)). The same seed gives the same grooves; mutation edits single hits, nudges them by a sixteenth, re-accents them or regenerates a lane.