LFO

lfo(opts)

Returns an LfoSpec that can be passed to modulatable machine parameters (e.g. cutoff on vasynth). The LFO runs as a per-note OscillatorNode inside Web Audio API.

lfo(opts: {
  rate: number;          // cycle length in beats (4 = one cycle every 4 beats)
  min: number;           // minimum value (Hz)
  max: number;           // maximum value (Hz)
  shape?: 'sine' | 'tri' | 'saw' | 'square';  // default: 'sine'
  offset?: number;       // start phase offset: 1=max, -1=min, 0=center (default). sine only.
}): LfoSpec

The lfo function is injected by the engine at runtime — it reads the current BPM automatically, so rate is always expressed in musical beats rather than seconds.

Example

function* song(ctx) {
  const synth = vasynth({
    wave: 'sawtooth',
    cutoff: lfo({ rate: 4, min: 300, max: 3000, shape: 'sine' }),
    gain: 0.5,
  })
  const key = scales(4, 'A3:minor')
  while (true) {
    yield cast(synth, key, seq(4, '0,2,4,3'), ctx)
  }
}

Parameters

Parameter	Type	Default	Description
rate	number	—	LFO period in beats. 4 = one full cycle every 4 beats.
min	number	—	Minimum modulation value.
max	number	—	Maximum modulation value.
shape	string	'sine'	Oscillator shape: sine, tri, saw, square.
offset	number	0	Start phase offset. 1 = start at max, -1 = start at min, 0 = center. Applies to sine only. Range: −1 to 1.

Modulatable parameters

The following parameters accept an LfoSpec in addition to a plain number:

Machine	Parameter
vasynth	cutoff

Notes

• The LFO oscillator starts fresh on every note trigger (per-note).
• BPM is captured at the moment the machine is created inside the generator loop, so tempo changes take effect from the next cycle.