The Krell patch uses a sample-and-held random pitch plus a self-triggering envelope to play itself

The Krell patch, popularised by synthesist Todd Barton, is a canonical self-playing modular technique. A random voltage is sampled (sample-and-hold) to set a new pitch for a VCO on each trigger, and each trigger also fires an envelope through a VCA so the note swells and fades; crucially the envelope’s own end-of-cycle can re-trigger the next note, so the patch clocks itself with no fixed grid and note density follows envelope length. The result is an irregular, ambient, meditative stream of notes. Its name references the all-electronic score (by Bebe and Louis Barron) of the 1956 film Forbidden Planet. Pitches are usually quantized to a scale to stay musical.

Examples

// Krell roles: // random source -> S&H -> VCO (V/oct) : one held random pitch per trigger // trigger -> Envelope -> VCA, env-end -> next trigger : self-clocking, note blooms and fades

Assessment

Explain why a Krell patch sounds less mechanical than a fixed-sequencer patch, identify what sets each note’s pitch and what sets the timing, and name the module you would add to keep pitches in a scale.