Photo: Grin, CC BY-SA 4.0 / Wikimedia Commons, Krakenimages.com / Shutterstock
The sound has been known to cause feelings of anxiety and panic.
By NyRee Ausler — Written on Mar 05, 2023
Most of us are familiar with optical illusions. They make our eyes and brains question whether they are seeing things as they truly are, or creating our own version of what we see.
Similarly, an auditory illusion can trick your brain and your ears into believing they hear certain things. They are false perceptions of real sounds generated by outside stimulus.
One such audible illusion is called the Shephard tone, a sound named after cognitive scientist Roger Shepard, who created it in addition to an optical illusion called the Shepard table.
What is a Shepard tone?
The Shepard tone, also known as the Shepard scale, is a sound design or a set of sine waves that creates the illusion of a consistent and never-ending tone that will rise or fall.
It is achieved by overlapping notes that go up or down just one octave but varying in volume. As each scale fades in and out, the beginning and end of each become indistinguishable and seemingly start to continually ascend or descend.
The Shephard tone creates a way to build conflict or ramp up tension. In film, it is intended to give a sense of discomfort or indicate that trouble is afoot.
It is one of the sound effects that creates a foreboding sense that morphs into a haunted effect, building anticipation and anxiety.
A great example can be found in the 1996 "Super Mario 64" video game.
Visually creating a Shepard scale would produce an image that looks like a staircase that goes on forever. It’s also referred to as a "Musical Barber Pole" or "The Sonic Barber Pole" due to comparisons to the infinite diagonal lines.
Like a barber pole, the scales have the illusion of continuously moving up or down, but in actuality are simply looping around and around.
French composer Jean-Claude Risset created an alternate form, which he coined as the Shepard-Risset glissando. In his version, the sounds move smoothly from one to the next to create a more haunting version.
How does the Shepard tone work?
The Shepard tone is one of the most popular audio illusions known.
The series of notes spaced an octave apart and variances in volume give the listener the impression that it is an endless sound when played in a loop.
Its tones lure our brain into making errors in perception. Although it is simply a series of short, repeated patterns, we hear it as a continuous single pattern that keeps changing pitch.
Why does a Shepard tone cause anxiety and panic?
The effects of music on human emotions is still being studied, but life experiences tell us that it has a profound impact.
What has been proven is that music increases blood flow to the brain regions that house our emotions. Our limbic systems are very responsive to music. Music also gives listeners a dopamine boost.
Music is used to help regulate moods, so it stands to reason that the Shepard tone, which is meant to make listeners anxious or panicky, does exactly what it was meant to do.
Some TikTokers have subjected themselves to what they consider to be "audio torture," playing the Shepard tone on a loop for hours on end.
TikToker Sean Andrew documented his experience listening to the sound for 10 hours.
Andrew reported that he experienced chest pressure, anxiety, racing thoughts, elevated heart rate, and ringing in his ears after playing the sound for 5 hours.
The Shepard Tone in Music & Movies
Christopher Nolan used the Shepard tone in his 2008 movie, "The Dark Knight." The sound of Batman’s motorcycle, the Batpod, has sound effects that demonstrate the constant rising and falling of a single note.
In the 2017 Hans Zimmer movie, "Dunkirk," the Shephard tone was used to create the rising and falling sound of an orchestra to create drama and ramp up the tension.
The Shephard tone is used a lot in music, namely by pop groups like Pink Floyd and The Police. Generally, it is used to elevate tension just before a kick.
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NyRee Ausler is a writer from Seattle, Washington, and author of seven books. She covers lifestyle and entertainment and news, as well as navigating the workplace and social issues.