Spin Up

How it's made

Source

a rotor accelerating from standstill. Its tone is a sawtooth harmonic stack whose fundamental rises from 12 % of the top pitch to the top pitch along an ease-in curve (slow start, accelerating finish), plus a detuned second voice (+0.4-0.8 %) for the beating of an imperfect rotor and a sub octave.

Body

the housing acts as a low-pass whose cutoff opens from ~250 Hz to 2-7.7 kHz as speed rises, so harmonics appear one by one; a mild resonance (Q 1.6) follows the sweep and adds the mechanical whine.

Air

pink noise through a band-pass at 7 x the fundamental stands for blade-pass turbulence; it grows with speed squared and is high-passed at 150 Hz.

Envelope

level rises with rotor speed (roughly quadratic), holds at full speed for the last 12 %, then a 60 ms fade ends the one-shot cleanly after a 10 ms fade-in that avoids a click.

Variation

`rng` shifts the top pitch by +-2 % and the detune; length, top pitch, brightness, air and grit change the character; presets cover a turbine, a disk drive, a heavy flywheel and a quick charge.

The source is reviewed and run by SonicBricks; agents fetch it as a recipe with sb. It is not published on this page.