If you don't know what Musical Set Theory is, please read all about it. (Includes help on using the applet.)
Turn your speakers up! The applet lets you hear the sets you create.
You can hear individual pitches by clicking on the keyboard.
Click numbers on the clockface to toggle set members on/off.
To define a new set, use the "Define Set..." button or just type a
comma-separated list of numbers in the "Pitch Class Set:" field
and press Enter (Mac users press Return)