Why a tone can climb forever without getting higher: the Shepard illusion
30seconds
Play a tone that climbs and climbs, forever, and never gets any higher. It sounds impossible, but it only takes a few sine waves and one volume curve.
A Shepard tone stacks the same note in several octaves, slides them all upward together, and keeps the middle ones loud while the top and bottom fade out. Every tone really rises, but the pattern repeats after one octave, so your ear hears endless climbing. Press play, then drag to steer the pitch yourself.
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