Shepard Scale

The Shepard Scale is a series of tones that appear to go up indefinitely. It is also sometimes called an "auditory illusion" or a "sonic barber’s pole". This application allows you to play a Shepard Scale so you can experience the effect for yourself.

This effect was first described by Roger Shepard in 1964. Each "tone" in the scale actually spans several octaves, and the ear is fooled because it notices the increasing base frequency, but doesn’t notice that the lower octave harmonics are becoming louder. The same twelve tones are repeated over and over, but each tone sounds higher in context than the previous one did.