A phenomenon in the perception of musical tones that are clearly defined in terms of pitch class (the twelve notes of the octave that are normally labelled C, C#, D, … , B) but are ambiguous as regards the octaves to which they belong, each tone being composed of equal sinusoidal waves from octaves spanning the auditory range. If one such ambiguous tone is followed by a second, separated from the first by a tritone, then the sequence is clearly perceived as either rising or falling by half an octave, although the stimulus tones lack the cues required to determine pitch. It is a surprising phenomenon rather than a true paradox. See also auditory illusion, auditory staircase illusion. Compare melodic paradox, semitone paradox.