György Ligeti Edition 5: Mechanical Music - Barrel Organ; Metronomes; Player Piano; 2 Player Pianos

Process music is a movement in which a composition is generated by a clearly defined procedure or rule-set. Sometimes this procedure is made audible—so the listener can follow the gradual changes as they unfold—and sometimes the process remains hidden behind the surface of the sound. Typical processes include phasing (two identical patterns drifting out of sync), additive or subtractive procedures (expanding or contracting a pattern by fixed steps), iterative feedback (repeating an operation so the output becomes the next input), permutations, stochastic or probabilistic rules, or instruction-based performance systems. The aesthetic ranges from hypnotic and pulse-driven to fragile and static, but the core idea remains: the music arises from the process.

Mechanical music is music generated by self‑playing instruments that read and reproduce music through purely mechanical means, with no major electronically controlled elements. Typical carriers include pinned cylinders and discs (music boxes and barrel organs), perforated paper rolls (player pianos), and cardboard music books (fairground and dance organs). Sound is produced by physical actions—plucked steel teeth, organ pipes driven by bellows, struck strings or percussion—set in motion by clockworks, cranks, weights, or pneumatic actions. The result is a precise, repeatable performance that reflects both the arrangement encoded on the medium and the tonal character of the instrument.