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The Shepard Tone Is A Sonic Barber Pole

A Shepard tone is a sound that seems to go up or down in pitch forever. At least it seems to, but it's only an illusion.

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Why It's Noteworthy

Take a listen to the Shepard Tone in the video below. Sounds like the pitch is creeping up and up and up and up, forever, doesn't it? In fact, the sound is simply an auditory illusion — one that has been described as a "sonic barber pole." In the same way that the classic red-and white-striped barber pole seems to perpetually spin upward when it's just staying still, Shepard tones seem to infinitely rise in pitch, when it fact they are rising, then dropping an octave and rising again, on infinite repeat. So why does it feel like the sounds is always getting higher? This tone is made of multiple sine waves that trick our brain. Even though the sounds in the tone reach a certain point and then hop back down an octave and start again, our brains don't hear that jump. Instead they hear the tones rising or falling forever.

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Why It's Worth Sharing

For anyone who loves optical illusions, audio illusions are another great (but lesser known) discovery. And now that you know about them, you may start to notice Shepard tones in pop culture, since they are a great vehicle for setting a mood. Like in The Dark Knight and The Dark Knight Returns. As the films' sound designer Richard King told the Los Angeles Times: "The Batpod is slicker and more refined. I used the concept of the Shepard tone to make the sound appear to continually rise in pitch. The basic idea is to slightly overlap a sound with a distinct pitch (a large A/C electric motor, in this case) in different octaves. When played on a keyboard, it gives the illusion of greater and greater speed; the pod appears unstoppable."

Editors' Picks: Our Favorite Videos About Audio Illusions

Hear The Shepard Tone Illusion

Take a listen. You won't believe your ears.

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Key Facts In This Video

  1. The Shepard tone is a noise that seems to continuously rise or fall in pitch forever. 00:17

  2. The Shepard tone is referred to as a "sonic barber pole." 00:36

  3. People in the United States pronounce the word "adidas" differently from the rest of the world. 01:17

4 Weird Audio Illusions

There's more where the Shepard tone came from.

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Key Facts In This Video

  1. The speech-to-song illusion refers to when a repeated phrase begins to sound like a song. 00:34

  2. Your response to the tritone paradox may be based on where you're from and the speech patterns of your childhood. 02:23

  3. The phoneme restoration effect makes your brain think it heard a complete word or sound, when in fact parts were missing. 04:35

Can You Trust Your Ears?

How do audio illusions work?

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Key Facts In This Video

  1. The McGurk effect refers to how visuals can change your perception of the same sound. 00:40

  2. Your location and language can play a role in determining the kinds of tones you hear. 01:46

  3. The Shepard Tone Illusion makes it seem like a series of rising pitches continues to rise higher and higher when replayed. 02:40

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