A modular kick drum is synthesized by modulating a sine wave's pitch downward with a fast envelope

The classic analog kick drum technique uses a sine (or near-sine) oscillator at a low frequency. A short, fast-decaying envelope is routed to the oscillator’s FM (pitch) input to create a rapid pitch drop at the transient — the ‘punch’ of the beater striking. A second envelope on the filter cuts the kick short, shaping the body length, and adding VCF drive distortion gives harmonic grit to the otherwise pure sine. By changing the envelope settings you make the kick and the pitch dive different lengths, shifting the character from a long 808-style thud to a tight 909-style snap.

Examples

VCV Rack kick patch: VCO-1 (sine, low freq) → VCF (with drive) → Mixer. ADSR1 (short attack, short decay) → VCO-1 FM input for the pitch dive. ADSR2 → VCF FREQ to cut the kick short. Increase ADSR1 decay for an 808-style long pitch sweep; decrease for a 909-style snap.

Assessment

What two envelope connections shape a modular kick? Explain how changing the pitch-envelope decay transforms the character of the kick from 808 to 909 style.