Undertone-based keyboard

Undertone series. If you divide a string or wind instrument (but apparently not a xylophone-like instrument[1][2]—see integer xylophone) into equal parts, these are the notes you get.

A
A
D
A
F
D
B
A
G
F
E-half-flat
D
C-half-sharp
B
A-sharp
A
G-sharp
G
F-sharp
F
E
E-half-flat
D-sharp
D

If scripts are enabled and working and you have a keyboard, you can use the number keys to play notes, [-] and [+] to change which notes the number keys play. You can also click or tap the keys.