Technology has arrived that lets us see why, exactly, we like or dislike a piece of music. A Princeton University composer, Dmitri Tymoczko, says traditional Western music is attractive partly because it obeys basic music-theory rules of "voice leading"--the way notes move from one chord to the next. (The rules say the steps should be fairly small.) He created a computer program that vividly shows how far a piece of music diverges from these rules.

In the image, generated by Tymoczko's program, each ball represents a three-note chord. The farther apart the balls are, the farther the voices have to jump between chords. As a song plays, another ball moves around the cone. If it moves in a circle, a chord pattern is repeating. If it moves from the cone's tip to its base, a piece is progressing toward dissonance.