Here are two examples of scales that demonstrate circularity in pitch judgement. The first is a discrete scale of Roger and Shepard. The second is a continuous scale of Jeanne Claude Clisse
One of the most widely used auditory illusions is Shepard's (1964) demonstra pitch circularity, which has come to be known as the "Shepard Scale" demonstration. The demonstration uses a cyclic set of complex tones, each composed of 10 partie separated by octave intervals. The tones are cosinusoidally filtered to produce the level distribution shown below, and the frequencies of the partials are shifted up in steps corresponding to a musical semitone (~6%). The result is an "ever-ascending scale, which is a sort of auditory analog to the ever-ascending staircase visual illusion