Motorcycle Pass

How it's made

Source

four-stroke exhaust pressure pulses; a four-cylinder engine fires at RPM / 30 Hz. A 270-degree twin instead has two unequal-spaced firings per 720-degree cycle (RPM / 120 Hz). Phase-related Fourier partials model these pulses, with seeded 0.35% combustion-speed wander.

Body

broad exhaust radiation around 650 Hz and 2.2 kHz weights the partials; no narrow resonances. Firing-modulated combustion noise (180-4200 Hz), intake rasp and half-order crank vibration add body.

Motion

a straight 24-60 m/s trajectory at 2-14 m clearance includes acoustic propagation delay. Pitch follows 343 / (343 + radial velocity); inverse-distance gain, air absorption and pan share it.

Envelope

the bike reaches the listener at 1.5 s; clearance / speed sets the sharp near-field swell. An 18 ms onset protects the waveform; a smooth departure taper reaches silence at 3.88 s. RPM rises 14% on approach, then eases; a short air wake trails closest approach by 65 ms.

Layers

a narrow moving engine leads; independently seeded tyre hiss and low wake remain subordinate. Exhaust radiation is slightly stronger behind the bike. No reverberation is embedded.

Variation

seeded pulse phase, RPM offset within 0.6%, drift and independent turbulence streams. Presets cover a high-rev sport pass, uneven twin, distant road and very close fast pass in reverse.

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