The Shepard Tone creates the illusion of continuously swelling sound, which can build tension or suspense. Find out how it works in this breakdown.

Cover via Warner Bros.



The Shepard Tone. If you’ve never heard of this term, I can almost guarantee you’ve heard the tone itself. The term refers to an auditory illusion of a sound that continually ascends (or descends) in pitch.

The tone is a sound that comprises multiple sine waves separated by an octave and layered on top of each other. In essence, there is a high-pitched tone, a middle-pitched tone, and a low-pitched tone that all rise in pitch until they loop back to the start. By the end of the track, the highest-pitched tone has become quiet, the middle-pitched tone stays loud, and the low-pitched tone has become louder. Because you can always hear two tones rising in pitch, your brain skips the loop and believes the tone is infinitely ascending.



Image via Vox.

In Vsauce’s video below, he explains another way to think about how the Shepard Tone works. Think of the three tones working in alternating roles. For example, the highest-pitched tone will drop down an octave and become the lowest-pitched tone, but since we can still hear the other two tones rise, we think the sound is ascending infinitely.

In recent years, one of the most famous uses of the Shepard Tone was Batman’s Bat-Pod in The Dark Knight (see 4:46)

Richard King, the sound designer behind The Dark Knight, said that “Chris [Nolan] had the idea that it should never shift, that it should keep ascending in pitch like an unstoppable force, we had an idea to use a concept called The Shepard Tone.” The team later captured the sounds from electric race cars and Tesla models to find the base pitch to create the Bat-Pod’s Shepard Tone.

Creating Tension

The sound illusion is ideal for film and game sound effects, but what about using the concept to create tension in a movie score? Christopher Nolan demonstrates this in the recently released action thriller Dunkirk, and thankfully we have a video essay breaking down the technique. Surprisingly, the video essay was produced by Vox, an organization that usually produces videos on news and international subjects. The top commenter has playfully said, “Not sure if I’m watching Vox or Nerdwriter1” because the essay is as well-produced as many other film theorists’ works on YouTube.

The video breaks down how composer Hans Zimmer has incorporated the Shepard Tone into the score, which creates an everlasting sense of tension throughout the film.

In an interview with Business Insider, Nolan said the following:

There’s an audio illusion, if you will, in music called a ‘Shepard tone’ and with my composer David Julyan on The Prestige we explored that, and based a lot of the score around that. It’s an illusion where there’s a continuing ascension of tone. It’s a corkscrew effect. It’s always going up and up and up, but it never goes outside of its range … And I wrote the [Dunkirk] script according to that principle. I interwove the three timelines in such a way that there’s a continual feeling of intensity. Increasing intensity. I wanted to build the music on similar mathematical principals. So there’s a fusion of music and sound effects and picture that we’ve never been able to achieve before.

Nolan has certainly mastered several cinematic techniques (such as nonlinear storytelling), and I think it would be a safe bet to add The Shepard Tone to that list.

What are your thoughts on the Shepard Tone? Let us know in the comments.

If you need a Shepard Tone for your next project, you can always find one in the PremiumBeat SFX library.