Shepard Tone

A psychoacoustic auditory illusion created by layering sine waves separated by octaves, producing the paradoxical perception of a tone that continuously rises (or falls) in pitch indefinitely, yet cycles back without apparent discontinuity. Named after cognitive scientist Roger Shepard, this technique is valuable in accessibility sonification because it allows continuous representation of circular or cyclic quantities—such as compass direction, angle, or rotation—without the jarring pitch jumps that occur when mapping 360 degrees back to 0 degrees using conventional pitch encoding. Shepard tones enable blind users to perceive smooth oscillations and rotations in audio representations of spatial data.