Dev builds AI music theory system: GPT-6 composes a full Bach-style fugue in one prompt

HankYeomans · x · 2026-09-10

Developer @doodlestein spent months building a closed-source AI music theory system: a Rust CLI tool mtdt (handling import/export and mechanical manipulation of MIDI, PDF, MusicXML, audio, etc.) plus a large skills library grounded in academic music theory.\n\nUsing GPT-6 Astra with mtdt and the relevant skills, a single prompt produced a complete Bach-style fugue — with no external software besides mtdt, including a print-ready PDF score. The system can also write theory-grounded counterpoint for a given melody, and much more. @aug5thmusic called it the most impressive musical feat ever seen from an LLM.

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