Projectile Whiz

How it's made

Source

a small projectile moving at transonic speed shears the air into a thin turbulent wake. It is broadband turbulence (white noise), strongest above 1 kHz, plus a faint tonal whistle from vortex shedding.

Body

the received spectrum is a narrow band (Q ≈ 5) whose centre is Doppler-shifted: it starts at about f0 × 1.5 while the object approaches, passes through f0 at closest approach and falls to f0 × 0.55 as it recedes, with the steepest drop right at the pass (about 3:1 overall). A second, wider band (Q ≈ 1.5) one octave lower adds the body of the wake; a short low thump at the pass is the pressure wave.

Envelope

the level rises as 1/distance over about 0.15 s, peaks at 38 % of the length and decays quickly, with air absorption darkening the tail; the whole event is about 0.5 s.

Space

the sound crosses the stereo field with equal-power panning, from one side to the other, moving fastest at the pass.

Variation

`rng` shifts pass time, centre frequency and whistle tuning by a few percent; parameters set speed, pitch, closeness and whistle; presets switch between a near miss, a distant pass, a ricochet-like whine and a slow dart.

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