The 21-key edition, heard before it ships. A player on the on-screen keyboard
already gets the right hand alone in a window that follows the piece — and
across the catalog only 6 of 148 pieces are playable that way: from
Passacaglia on, the board octave-jumps every few seconds and the right hand
starts playing chords a mouse cannot strike at all (one pointer).
js/keys21.js answers both by choosing what the player is asked to
hit. Both of its steps cost music, so listen: 1/2/3 swap
arrangement mid-playback on one clock, so you hear the same bar written
and folded a second apart.
arrangement
listenspace = play/stop · your hand on the player bus, the ghost hand quieter behind it
This piece on 21 keys
Melody as written vs folded
right hand as writtenyou play, unchangedyou play, folded an octavehanded to the ghost handthe fixed 21-key window
Where the folded line crosses the written one, the fold reversed a melodic
step — that is the “contour flips” number, and the one worth hearing.
The whole catalog
runs the real transform over every ready piece — one song.json each, so give it a minute