Feeding an analog video signal into an audio amplifier makes a fixed-pitch drone whose overtones encode the image

An analog composite video signal is a continuously varying voltage — roughly line level (~1 V peak-to-peak) — carrying synchronisation pulses and line-by-line brightness data. Fed into an audio amplifier’s input, it bypasses video decoding and is heard directly. The sync frequency sets a fixed fundamental pitch, unwavering as long as the camera runs normally, so camera movement does not change the pitch. The overtone structure, however, is generated line by line from image brightness and complexity, so timbre changes with what the camera sees: panning between a bright wall and a dark corner shifts the partials, and a rotating object (fan, turntable) creates interference patterns between its rate and the frame rate. Boundary condition: the fundamental is fixed by the frame/sync rate, not the image — to change pitch you must change the frame rate itself (e.g. hacking the clock crystal), which produces a simultaneous visual glitch and pitch shift. Video feedback (camera aimed at its own monitor) layers the effect iteratively.

Examples

Connect a camcorder’s composite output to a mixer/amp line input and hear the drone. Aim at a white card on a turntable at 33 vs 45 RPM, or at a rotating fan, to hear interference between frame rate and rotation. Pan between a white wall and a dark corner: the bright area adds high partials. Precedent: David Behrman’s Cloud Music used photocells reading monitors to drive oscillator pitch.

Assessment

Why is the fundamental pitch fixed regardless of camera movement while the timbre changes? What determines the overtone structure? What would happen to the pitch if the video frame rate were doubled?