Claude wrote every line of an acid techno track; human ears were the fitness function

ColossalCosci · reddit · 2026-11-15

A Reddit user released Jollas Phase, a 90s-style acid techno track fully written by Claude in the live-coding environment Strudel. Since Claude can't hear audio, the human acted as the fitness function:

Acid Seeker setup

Claude built an interactive evolutionary search for TB-303 basslines using rules from a producer's guide (root-note starts, simple repetitive patterns, accents open the filter, slides into octave jumps), plus a style profile learned per-round (density, repetition, octave jumps, slides, syncopation, tension).
Tens of thousands of patterns searched; each round showed 4 candidates as Strudel links, scored 1–5, with letters shuffled from round 3 to prevent ordering bias.

What it learned: converged on dense, rolling, repetitive lines with few slides; a polymetric 12-step variant scored lowest twice and was dropped; exactly one pattern earned a 5, placed at the climax.

Final track: 2:51 at 135 BPM in A minor with intro, groove, two drops, a break, clap-roll rise and climax; rendered offline via Strudel in a headless browser in chunks and mastered to −12.6 LUFS. The cover maps that evening's real moon phase over Helsinki—16 slices = 16 steps, brightness = accents. The video reads all 1,440 bass notes and 320 kicks from code, frame-synced to audio.

Track, video, and a two-voice essay ("who is the artist when one of you can't hear?") are free; Strudel runs in any browser.

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Claude wrote every line of an acid techno track; human ears were the fitness function

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