A basic hi-hat patch routes white noise through a highpass filter and a VCA controlled by a decay-only envelope

The hi-hat sound is built from noise (all frequencies) filtered to remove low energy, then shaped by a very short decay envelope. White noise → highpass filter (removes the low-frequency body that would sound like a kick or snare) → VCA → audio out. The VCA is controlled by a decay envelope set to a short value (10–50 ms for a closed hat, 100–300 ms for open). This demonstrates that percussion synthesis does not require pitched oscillators: noise + filter + short decay envelope covers hats, cymbals, and shakers. The pattern also shows that a decay-only envelope (no sustain phase) is simpler and sufficient for most one-shot percussion.

Examples

Noise source → HPF (cutoff ~3 kHz) → VCA; Decay envelope (30 ms) → VCA CV; Gate from drum sequencer → envelope gate. Result: crisp hi-hat click on each step.

Assessment

Explain why a highpass filter rather than a lowpass filter is used in a hi-hat patch; then describe what would happen if you replaced the decay envelope with a 200 ms gate from a sequencer.