[math-fun] Shepard's tones

Steve Gray wrote:

A few decades ago I visited the A.I. lab at Stanford and Les Earnest showed me around. He demonstrated something he called the "ever-rising tone." It was most impressive. Do you have any idea where I could get a copy of it (in almost any form, audio or digital)?

It was probably what is usually called "Shepard's tones" from a 1964 paper by Roger N. Shepard, "Circularity in Judgments of Relative Pitch" Google lists many online versions of it, e.g., http://www.noah.org/science/audio_paradox/ George http://www.georgehart.com/