In a standard 12-note keyboard octave, the frequency of one note is always half the frequency of the note one octave above it. So middle C, or C4, has a frequency of 261.626 Hz, and C5 is 523.251 Hz. Also, the frequency ration between each successive note is always the same, which means that they are of equally tempered tuning.
The normal 12-tone equal temperament keyboard octave is also called 12-TET. Well, over at Academo, a free, open-source hub for interactive educational demos, there’s an experimental 19-TET keyboard that you can play with either your mouse or your QWERTY keyboard.
As the 19-TET name indicates, this is also an equal-tempered keyboard but with seven notes added. The additional notes come by way of shorter-length grey keys that are “flats” added to the black-key sharps. (Of course, in the 19-TET the “flats” and “sharps” don’t sound the same.) Also, and extra “E#” and “B#” have been added to make a total of seven black keys.
I found it really interesting and fun to experiment with chords and note relationships on the 19-TET. I would love to have this tool for playing my virtual instruments in a DAW environment. What do you think?
Academo also has a Music section with other demos. It’s still sparse, as it is the newest category added to the site. Right now there’s a spectrum analyzer for uploaded files and an amplitude modulation demo. We hope to see more interactive music pages soon.