SynthHihat — Hi-Hat Engine

Files

static/js/synth/engines/hihat.js

Signal Path

noiseMix ──→ noiseBuf ──→ highpass (highCut) ──→ ng ──→ noteGain ──┐
                                                                     │
metalMix ──→ noiseBuf ──→ bandpass (metalFreq, metalQ) ──→ mg ──→ noteGain ──→ chain.input
                                                                                    │
                                                              filter → distortion → EQ → compressor → clarity → limiter → masterGain

Modules

ID	Type	Description
Noise	source	Noise mix + decay params
Metallic	source	Ring modulation params (freq, Q, mix, decay)
Filter	processor	High-pass (note: HPF, not LPF like other engines)
Distortion	distortion	Waveshaper pipeline
EQ	source	3-band EQ
Compressor	processor	Dynamics compressor
Clarity	processor	Mud/air reduction
Volume	master	ADSR envelope
Normalize	builtin	Peak normalization

Parameters

Param	Range	Default	Description
`noiseMix`	0–1	0.8	Main noise level
`noiseDecay`	0.01–0.5 s	0.08	Noise decay time
`highCut`	2000–20000 Hz	7000 Hz	High-pass cutoff for main noise
`metalMix`	0–1	0.4	Metallic ring level
`metalDecay`	0.01–0.5 s	0.06	Metallic ring decay
`metalFreq`	2000–12000 Hz	6000 Hz	Bandpass centre for metallic ring
`metalQ`	0.5–20	5	Bandpass resonance (ring intensity)
`filterCut`	200–20000 Hz	6000 Hz	High-pass filter cutoff
`clarity*`	—	—	See clarity module docs
`compThreshold`	–60–0 dB	–12 dB	Compressor threshold
`compRatio`	1–20	6	Compressor ratio
`volAttack`	0.001–0.02 s	0.001	Volume attack
`volDecay`	0.01–0.3 s	0.06	Volume decay
`volSustain`	0–0.3	0	Volume sustain
`volRelease`	0.005–0.2 s	0.01	Volume release

Differences from Other Engines

Filter is high-pass (not low-pass). Used to cut low rumble from the noise.
filterCut default is 6000 Hz (not 20000). Hi-hat sound inherently cuts lows.
Compressor is more aggressive (threshold –12 dB, ratio 6:1) to tame transient spikes.
Two separate noise sources — one for the main hi-hat sound, one for the metallic ring.

buildLiveChain

Uses the unified backward loop. The filter module's inline build creates a high-pass BiquadFilter (not low-pass).

trigger

Creates per-note noteGain with AD envelope, then creates: - Main noise through high-pass filter (cutoff = highCut) - Metallic ring noise through resonant bandpass (frequency = metalFreq, Q = metalQ)

Both noise sources hit noteGain which feeds chain.input.

Key Design

The main noise provides the broad "chch" hi-hat sound, while the metallic ring adds a tuned resonant layer that gives the hat its character and pitch. The separate highCut filter on the main noise (different from filterCut in the processor chain) lets you shape the noise independently before it hits the main processor chain.