Procedural sound synthesis layers independent filtered noise generators to build one complex texture

In procedural audio design, complex natural sounds (fire, wind, rain) are built by summing several independent generators, each responsible for a distinct spectral band or texture layer. Filtering a raw noise source in different ways extracts complementary characters: low-pass for crackle, band-pass for roar/rumble, high-pass for hiss. Per-layer amplitude scaling balances the mix before summing (Farnell’s fire patch scales its crackle, hiss and lapping layers at 0.2, 0.3, 0.6, then applies a 0.2 master gain). This layered approach mirrors the physics of the modelled sound: fire simultaneously crackles (transient events), hisses (turbulent air), and roars (low-frequency convection). The result is richer than any single source and is straightforwardly parameterised — each layer can be modulated independently in response to game state or performance control.

Examples

Pd fire patch (practical 11): crackle = noise -> lop~ / env~ / bp~ 4000 (0.2); hiss = noise -> hip~ 1000 -> amplitude modulation (0.3); lapping = noise -> bp~ 30 5 -> clip~ -> hip~ 25 (0.6); summed and scaled by a 0.2 master gain.

Assessment

Given a description of rain sound (drops, steady hiss, occasional rumble), sketch a three-layer procedural patch: name the filter type for each layer, the approximate cutoff, the shared source, and a relative amplitude for each layer.