An overdriven DFM1 filter self-oscillates into a warm drone that layers across the harmonic series

DFM1 (a digitally modelled analogue filter from sc3-plugins) produces a gorgeous warm tone when overdriven, distorting softly the harder it is driven — pushing resonance well above 1.0 makes it self-oscillate at its tuned frequency. For a drone, feed a sine at the root pitch through DFM1 and slowly modulate resonance around 1.0 with a very slow control-rate oscillator (e.g. SinOsc.kr(0.05).range(0.9,1.1)) to keep the tone alive without fatigue. Layering several DFM1 voices tuned to harmonic multiples of the root, each with a slightly different modulation speed, builds a full harmonic-series drone whose beats never repeat, needing minimal performer intervention during a set.

Examples

~drone = { DFM1.ar(SinOsc.ar(60), 120, SinOsc.kr(0.05).range(0.9,1.1)) }; — a self-oscillating bass drone; add voices at 2x/3x the root for the harmonic stack.

Assessment

Design a two-voice DFM1 drone (root plus a harmonic multiple) with staggered slow modulation, and explain why it sounds richer and more alive than a single sustained SinOsc.