FM modulation of a drum oscillator adds irregular attack-phase texture without noise

Pure sine-wave drum synthesis produces smooth, almost electronic-sounding transients. Adding a second oscillator as a frequency modulator — with its own very short envelope in trigger mode — injects brief inharmonic energy at the moment of impact before the fundamental takes over. This approximates the chaotic collision moment when a stick hits a membrane: complex, non-periodic motion that rapidly settles into the membrane’s resonant modes. The modulator envelope should be shorter than the carrier envelope so that the FM texture fades quickly, leaving a clean sine decay. This technique predates FM as a deliberate drum-synthesis strategy and is distinct from adding noise: FM produces pitched partials, noise produces broadband energy.

Examples

Operator: oscillator B modulates A with a very short trigger-mode decay envelope. Modulation index (operator output level) controls how harsh the ‘stick click’ is without adding continuous noise.

Assessment

Compare a pure sine kick to an FM-modulated kick by soloing the attack transient. Identify what spectral content FM adds that a single sine cannot produce. Then adjust modulation depth to go from ‘clean’ to ‘distorted click’.