Shepard tones

Shepard tones are auditory illusions that create the sensation of a continuously rising or falling pitch without actually getting higher or lower. They achieve this by layering several tones that are an octave apart, with their volumes faded so that as one tone fades out, another fades in at a higher or lower pitch. This overlapping effect tricks the ear into perceiving an infinite ascent or descent, even though the sound remains within a fixed pitch range. Shepard tones are often used in music, sound design, and psychological experiments to explore perceptions of pitch and infinity.