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Shepard Tone
Shepard Tone
An auditory illusion
An auditory illusion
Description:
This illusion creates the sensation of a continuously rising pitch (or a continuously dropping pitch, for it works the other way too).
Shepard Tone
Demonstration with Penrose Stairs:
Explanation:
The Shepard Tone is comprised of sine waves that are octaves apart from each another. All the waves are rising in pitch but every once in a while one or more waves (depending on the total number of waves) drop(s) an octave. Our brains don't perceive that because the rest of the waves continue to rise. This results in the production of a Sonic Barber Pole (which is basically a tone that rises in pitch seemingly forever). Therefore, it is also compared to the optical illusion of Penrose Stairs — an impossible object.
External resources:
1. https://techchannel.att.com/play-video.cfm/2011/10/10/AT&T-Archives-A-Pair-of-Paradoxes
2. http://yadegari.org/MasterThesis/node35.html
3. http://www.cycleback.com/sonicbarber.html