The Shepard-Risset Glissando

Construction of a Shepard scale The acoustical illusion can be constructed by creating a series of overlapping ascending or descending scales. Similar to the Penrose stairs optical illusion (as in M. C. Escher’s lithograph Ascending and Descending) or a barber’s pole, the basic concept is shown in figure 1. Each square in the figure indicates a tone, any set of squares in vertical alignment together making one Shepard tone. The color of each square indicates the loudness of the note, with purple being the