Shepard tones create endlessly rising pitch through shifting autocorrelation peaks

Evidence

Every step clockwise to the next note is an apparent semitone higher in pitch. There is a left shift of the autocorrelation peaks (which means they appear earlier in time and correspond to higher pitch), and there are small changes in their shape and height. The shift is just that required for the pitch to rise a semitone. When the first two tall peaks are about equal in height, they are an octave apart and both can be heard. Both tones rise in the next clockwise step up (both peaks shift left), but the peak closer to t = 0 (higher pitch) starts to diminish in height, gradually making the lower pitch more dominant even though each clockwise step raises the pitch of both peaks by moving them left. Eventually, new peaks moving from the right to left arrive, after 12 steps, to exactly reproduce the starting autocorrelation function. — Eric J. Heller, Why You Hear What You Hear- An…, 2121

Categorization

• XREF: The Shepard illusion and its autocorrelation mechanism connect to the reader’s auditory perception corpus on how the brain reconstructs pitch from temporal structure.