2. Rhythm Section

Nimbus has dedicated drum machines for kick, snare, and hi-hat. They use drum-mode seq strings (x = hit, . = rest) instead of scale degrees.

The three drum machines

function* song(ctx) {
  const kk = kick()
  const sn = snare()
  const hh = hat()

  yield cast(kk, 'drums', seq(4, 'x.x.x.x.'), ctx)
  yield cast(sn, 'drums', seq(4, '..x...x.'), ctx)
  yield cast(hh, 'drums', seq(4, 'x.x.x.x.'), ctx)
}

Pass 'drums' as the second argument to cast whenever you use a drum machine — pitch is ignored.

`kick` — bass drum

kick() is a synthesized bass drum based on a pitch-swept sine wave. Key parameters:

Parameter	Default	Effect
`pitch`	60 Hz	Starting frequency — higher = tighter, lower = boomy
`decay`	0.3 s	Length of the tail
`punch`	0.8	Transient click — higher = harder attack
`gain`	0.8	Output level

// Standard kick
kick()

// Tight and punchy (techno/house)
kick({ pitch: 80, decay: 0.15, punch: 1.0 })

// Deep and slow (hip-hop / trap)
kick({ pitch: 40, decay: 0.8, punch: 0.5 })

// High and clicky (dry click track)
kick({ pitch: 120, decay: 0.05, punch: 1.0, gain: 0.6 })

`snare` — snare drum

snare() combines a tonal body with a noise burst. Key parameters:

Parameter	Default	Effect
`tone`	180 Hz	Body frequency — higher = brighter crack
`snap`	0.9	Noise punch amount
`decay`	0.15 s	Length of the tail
`gain`	0.7	Output level

// Standard snare
snare()

// Tight crack (reggae / pop)
snare({ tone: 220, snap: 1.0, decay: 0.08 })

// Deep rimshot
snare({ tone: 140, snap: 0.5, decay: 0.25 })

// Snappy clap-like hit
snare({ tone: 300, snap: 1.0, decay: 0.04, gain: 0.8 })

`hat` — hi-hat

hat() is a metallic noise oscillator. Key parameters:

Parameter	Default	Effect
`decay`	0.05 s	Length — short = closed, long = open
`tone`	8000 Hz	Filter frequency — higher = brighter
`gain`	0.5	Output level

// Closed hi-hat (default — very short)
hat()

// Open hi-hat
hat({ decay: 0.35 })

// Ride cymbal feel
hat({ decay: 0.6, tone: 6000, gain: 0.4 })

// Shaker / ghost hat
hat({ decay: 0.02, tone: 10000, gain: 0.25 })

Drum patterns

Classic patterns

// 4/4 rock beat
yield cast(kk, 'drums', seq(4, 'x.x.x.x.'), ctx)  // kick on 1, 2.5, 3, 4
yield cast(sn, 'drums', seq(4, '..x...x.'), ctx)   // snare on 2 and 4
yield cast(hh, 'drums', seq(4, 'x.x.x.x.'), ctx)  // 8th-note hat

// Straight four-on-the-floor (house/techno)
yield cast(kk, 'drums', seq(4, 'x...x...x...x...'), ctx)  // 16th grid

// Trap hi-hat: dense 16th notes with gaps
yield cast(hh, 'drums', seq(4, 'x.xx.x.xx.xx.x..'), ctx)

Syncopation

Offset the kick or snare from the beat for groove:

// Syncopated kick (pushes beat 3)
yield cast(kk, 'drums', seq(4, 'x...x.x.....x...'), ctx)

// Reggaeton / dembow (kick on 1 and "and-3")
yield cast(kk, 'drums', seq(4, 'x.....x.x.......'), ctx)
yield cast(sn, 'drums', seq(4, '....x.......x...'), ctx)

Ghost notes with velocity

Add a (v:low) suffix to make a hit quieter (velocity 0–1):

// Snare with ghost notes — lowercase = implied low velocity in text, use w: for weighted
yield cast(sn, 'drums', seq(4, '..x...x.'), ctx)   // main hits

Polymeter — different loop lengths

When a drum sequence has a different beats value from the other patterns, it loops at its own rate. This creates evolving, interlocking rhythms automatically.

function* song(ctx) {
  const kk = kick()
  const sn = snare()
  const hh = hat()

  yield cast(kk, 'drums', seq(4,  'x...x...x...x...'), ctx)  // 4 beats
  yield cast(sn, 'drums', seq(3,  '..x.x.'), ctx)             // 3 beats — loops every 12 beats
  yield cast(hh, 'drums', seq(2,  'x.x.x.x.'), ctx)           // 2 beats
}

The kick, snare, and hat are now in 4:3:2 ratio — they realign every 12 beats.

Full rhythm section example

A complete beat with melodic bass:

function* song(ctx) {
  const kk   = kick({ decay: 0.25 })
  const sn   = snare({ snap: 0.8 })
  const hh   = hat({ decay: 0.04 })
  const ohh  = hat({ decay: 0.3, gain: 0.3 })
  const bass = vasynth({ wave: 'sine', cutoff: 600, attack: 0.01, release: 0.15, gain: 0.7 })
  const bKey = scales(4, 'C2:minor')

  yield cast(kk,   'drums', seq(4, 'x...x.x.....x...'), ctx)
  yield cast(sn,   'drums', seq(4, '....x.......x...'), ctx)
  yield cast(hh,   'drums', seq(4, 'x.x.x.x.x.x.x.x.'), ctx)
  yield cast(ohh,  'drums', seq(4, '......x.......x.'), ctx)
  yield cast(bass, bKey,    seq(4, '0,_,_,4,_,2,_,_'), ctx)
}

3. Melody & Harmony → — add chord progressions and multi-voice melody.