A
Shepard tone, named after
Roger Shepard, is a sound consisting of a superposition of sine waves separated by octaves. When played with the base
pitch of the tone moving upward or downward, it is referred to as the
Shepard scale. This creates the
auditory illusion of a tone that continually ascends or descends in pitch, yet which ultimately seems to get no higher or lower. It has been described as a "sonic
barber's pole".