I’ve had some fun over the last few days putting together a little toy called Musicle. It helps you understand a bit about how the Western musical scale is put together and why the notes are the way they are, using something called an Euler lattice.
Musicle gives you a screen with middle C in the middle and a grid of notes around it. Notes to the left and right are separated by a perfect fifth (frequency ratio 3/2), and notes above and below are separated by a major third (frequency ratio 5/4). Believe it or not, the usual Western scales and notes are generated simply by powers of 3 and 5 (and 2, for the octave).
Musicle lets you play the notes, on their own or in combination, by clicking on them. Hold Ctrl if you want to play several notes together.
One of the things that becomes apparent when you start exploring is that the notes don’t quite line up with each other the way your musical theory might have led you to expect. Musicle shows the nearest note name to each pitch, but it also shows the distance of that pitch from the “normal” even-tempered pitch, in cents (100ths of a semitone).
To make it easy to explore without odd jumps, I’ve used Shepard tones. You can turn this off at the bottom if you like, and you can also choose one of a very small number of instruments.