The Shepard Tone: Auditory Illusion


Sine Waves

This could possibly be written for iPsy, but I reckon it will feel at home here.

Audio is incredibly fascinating topic that covers maths, physics, music and cognitive/behavioural psychology. Upon watching a short BBC tech film at late midnight, I learnt about The Shepard Tone.

Named after Rodger Shepard, the Shepard tone is a sound consisting of a superposition of sine waves separated by octaves (an octave is the interval between one musical pitch and another with half or double its frequency). But what’s so special about the Shepard tone?

This superposition of sine waves separated by octaves creates an auditory illusion of a tone that perpetually ascends or descends, without it reaching a limit of it getting higher or lower.

Here’s an example of the Shepard tone. The sound seems to be forever falling down, even if you replay the same video!

The Shepard's tone is sometimes described as the Sonic's Barber Pole.

Also, it is referred to as the Shepard scale when played with the base pitch of the tone moving upwards or downwards.

You can find more out about it in the link below!

via http://www.cafemuse.com/soundgarden/perception/shepard.htm

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