Film Projector Loop

How it's made

Source

a spooled-film projector. A synchronous motor hums at the mains frequency (≈ 50 Hz with strong 2nd/3rd harmonics from the laminations); each frame a claw pulls the film down and a shutter blade cuts the light, so every frame produces one mechanical event: a 1–3 ms claw/sprocket click plus a softer gate knock about a third of a frame later.

Body

the click excites a small steel pallet (2–6 kHz, 15–40 ms) and the sheet-metal housing (hollow resonance 180–320 Hz, ≈ 30 ms); the film running over rollers adds a band-limited air "whirr" (0.5–3 kHz) that is amplitude-modulated at the frame rate by the shutter.

Envelope

clicks are instant-attack, exponential-decay; the whirr breathes at the frame rate; the hum is steady. Frames per second are an integer, so the 6 s loop always holds whole frames.

Flutter

the motor speed and the film tension wander slowly (0.4–1.2 Hz, ±1.2 % pitch): the hum pitch drifts, the whirr level wobbles and the click strengths fluctuate, as in a worn machine.

Variation

`rng` tunes each click, its level and sub-millisecond timing jitter; presets move frame rate, housing resonance, wear and the balance of hum, whirr and clicks.

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