The engine we could not borrow

The Yumeo MP-3 is a 1999 perceptual coder, and restoring it honestly meant encoding MPEG-1 Layer III — not decoding it, encoding it, with the era’s arithmetic intact. The swirl at low bitrate is not a defect to be cleaned away; it is the object under restoration.

An encoder is a tool like any other on the bench, and the bench prefers to borrow before it builds. But every Layer III encoder we could reach carried a licence that could not travel inside a sealed instrument. No fault of theirs — those licences protect a different kind of work. Ours simply could not use them.

So the bench built its own. First a reference in plain arithmetic, slow and readable, every table transcribed from the standard and checked twice. Then the working engine, held against that reference until the two produced the same bytes — not similar bytes; the same bytes. The reference stays in the case beside the tool, the way a conservator keeps the measurement beside the repair.

We have named it epicycle, for the small circle in the old orbital models — an elegant approximation the world outgrew, which still predicts beautifully. That seemed right for MP3.

The engine now drives the restoration at the bench, and it will carry the MP-3’s next issue. And because the licence problem it solved is not ours alone, the source is public: MIT-licensed, tests and reference included, at github.com/orreryarchive/epicycle. Take it, verify it, use it.

Note: Orrery is a work of fiction — the houses, the catalogue’s histories, and Iver Sandholm are invented. The encoder is not. It was written at this bench with AI assistance under human direction, and every claim in its repository can be re-proven from source. The instruments it serves are real software, really sold and supported. Only the story is a story — and we think the work is better for being checkable where it matters.