Pitch circularity

Pitch is often defined as extending along a one-dimensional continuum from high to low, as can be experienced by sweeping one’s hand up or down a piano keyboard.

Because the octave is the most consonant interval after the unison, tones that stand in octave relation, and are so of the same pitch class, have a certain perceptual equivalence—all Cs sound more alike to other Cs than to any other pitch class, as do all D♯s, and so on; this creates the auditory equivalent of a Barber's pole, where all tones of the same pitch class are located on the same side of the pole, but at different heights.

[2] When such complex tones are played in semitone steps the listener perceives a scale that appears to ascend endlessly in pitch.

A different algorithm that creates ambiguities of pitch height by manipulating the relative amplitudes of the odd and even harmonics, was developed by Diana Deutsch and colleagues.

[5] Using this algorithm, gliding tones that appear to ascend or descend endlessly are also produced.