> The PianoDisc versions are mp3s encoded with the right channel carrying MIDI to be played on the piano, and the left channel containing any accompanying music to be played through attached speakers (who doesn't want the harmonica on Piano Man?)

What a cursed format!

I don't understand what the designers were thinking of... 2000 Hz square wave on right channel? Seriously? Nobody would hear something suspicious and nobody would literally see it on spectrum analyzer. Maybe it's holdover from analog days and it was on casette tape before.

Also somebody reverse engineered it before - https://www.kinura.net/mid2pianocd/

So Fable probably just igested it from documentation of this software or some very obscure forum thread somewhere.