Shepard TonesClassical theories of music psychology regard the tone as a phenomenon consisting of two components, chroma (or "quality") and height (see Ch. 2 TONE for a more detailed discussion). According to this theory these two components are orthogonal. Recent research in music perception has begun to call this theory into question. For one thing, some recent psychoacoustical research show that the cyclical nature of tones is not necessarily restricted to the octave. For instance, some research has found that the precise interval of circularity may depend on the overtone structure of the tones themselves. Moreover, auditory illusions such as the Shepard-Tone is (chroma) already incorporates a notion of height. In this chapter we consider the Shepard tone and the notion of tone that it proposes.