engines/kick.js — SynthKick

The kick drum synthesiser. Defined as a SynthEngine object with 7 modules.

Modules

The modules array defines both the UI panels (order, labels, params) and the signal chain (processor order).

1. Pitch (source)

Param	Range	Default	Description
`pitchStart`	80–400 Hz	220	Initial oscillator frequency
`pitchEnd`	25–100 Hz	50	Final frequency after decay
`pitchDecay`	0.03–0.5 s	0.06055	Sweep duration
`sineLevel`	0–1	1	Sine oscillator level
`triangleLevel`	0–1	0	Triangle oscillator level
`sawtoothLevel`	0–1	0	Sawtooth oscillator level
`pitchCurve`	exponential/linear	exponential	Contour of the frequency sweep
`subMix`	0–1	0.5	Sub oscillator (sine, octave down) blend

Creates the main oscillator with a frequency ramp (exponential or linear), a gain envelope, and an optional sub oscillator at half frequency.

2. Transient (source)

Param	Range	Default	Description
`noiseAmount`	0–0.5	0.12	White noise burst volume
`noiseDecay`	0.003–0.08 s	0.015	Noise fade time
`clickTone`	200–2000 Hz	800	Pitched click frequency
`clickMix`	0–0.3	0.1	Click blend level

Generates a white noise buffer source and a sine oscillator click, both with exponential decay envelopes.

3. Distortion

Dynamic stage pipeline (see distortion.js).

4. Filter (processor)

Param	Range	Default	Description
`filterCut`	200–20000 Hz	20000	Low-pass cutoff (bypassed at 20000)

BiquadFilter node with type: 'lowpass'. When cutoff is at maximum (20000 Hz), the filter bypasses (returns input unchanged).

5. Compressor (processor)

Param	Range	Default	Description
`compThreshold`	–60–0 dB	–21.3	Compression threshold
`compRatio`	1–20	4	Compression ratio
`compAttack`	0.001–0.1 s	0.003	Attack time
`compRelease`	0.01–1.0 s	0.1	Release time

Wraps DynamicsCompressorNode with clamped parameter ranges. Wrapped in try/catch for browser compatibility — falls back to pass-through.

6. Volume (master)

Param	Range	Default	Description
`volAttack`	0.001–0.1 s	0.002	Time to peak
`volDecay`	0.05–0.8 s	0.3	Time to sustain
`volSustain`	0–0.5	0.05	Post-decay level
`volRelease`	0.005–0.5 s	0.05	Fade to silence

Schedules linearRampToValueAtTime on the master gain node. Total duration: max(0.5, attack + decay + release + 0.1).

7. Normalize (builtin)

Param	Default	Description
`normalize`	true	Peak normalise to –0.5 dBFS after render

Signal Chain

osc + sub + noise + click
  → [distortion stages]
  → filter (lowpass)
  → compressor
  → master gain (ADSR volume)
  → destination

After rendering, normalize is applied to the PCM samples if enabled.

Canvas Visualisations

Three envelope canvases are rendered in a dedicated Envelopes card below the waveform:

Canvas ID	Module	Curve
`env-pitch`	Pitch	Exponential decay of frequency from start to end
`env-volume`	Volume	ADSR amplitude envelope
`env-transient`	Transient	Exponential decay of transient amplitude

Rendering

The render function creates source nodes (oscillator, sub, noise, click) and connects them to chainInput (the first distortion stage or master gain):

render(ctx, params, stages, chainInput, dur) {
  // Pitch oscillator + gain
  osc = ctx.createOscillator()
  schedulePitch(osc, params, dur)
  osc.connect(oscGain).connect(chainInput)

  // Sub oscillator (if subMix > 0)
  sub.connect(subGain).connect(chainInput)

  // Noise burst (if noiseAmount > 0)
  noiseBufferSource.connect(noiseGain).connect(chainInput)

  // Click tone (if clickMix > 0)
  click.connect(clickGain).connect(chainInput)
}

Defaults

Loaded from static/js/synth/presets/kick.json at startup, falling back to engine.defaults:

{
  "params": {
    "pitchStart": 220, "pitchEnd": 50, "pitchDecay": 0.06055,
    "sineLevel": 1, "triangleLevel": 0, "sawtoothLevel": 0,
    "pitchCurve": "linear", "subMix": 0.5,
    "noiseAmount": 0.12, "noiseDecay": 0.015,
    "clickTone": 800, "clickMix": 0.1,
    "filterCut": 20000,
    "volAttack": 0.002, "volDecay": 0.3, "volSustain": 0.05, "volRelease": 0.05,
    "compThreshold": -21.3, "compRatio": 4,
    "compAttack": 0.003, "compRelease": 0.1,
    "normalize": true
  },
  "stages": [{ "type": "softClip", "amount": 0.01 }]
}

Built-in Templates

Defined in static/js/synth/presets/templates/kick.json:

Template	Description
None	No constraints, params set to defaults
Sine Kick	Sine wave, no compression, linear pitch, locked distortion
Hard Punch	Sawtooth wave, `subMix: 0.3`, hardClip distortion
Sub Heavy	Deep sub focus (`subMix: 0.85`), gentle saturation

Randomisation Ranges

Each module's randomise(param) function sets curated ranges. Locked params are skipped.

Section	Param	Range
Pitch	Start	120–350 Hz
	End	30–80 Hz
	Decay	0.05–0.35 s
	Sine/Triangle/Sawtooth	each 0.3–1 (at least one non-zero)
	Curve	random: exponential / linear
	Sub mix	0.2–0.8
Volume	Attack	0.001–0.06 s
	Decay	0.08–0.5 s
	Sustain	0–0.25
	Release	0.01–0.2 s
Transient	Noise	0.03–0.4
	Decay	0.004–0.06 s
	Click tone	300–1500 Hz
	Click mix	0.02–0.25
Filter	Cutoff	300–18000 Hz (log)
Compressor	Threshold	–40 to –10 dB
	Ratio	2–12
	Attack	0.001–0.05 s
	Release	0.02–0.5 s