What is the Shepard Tone?

Looking for a way to add tension to your EDM tracks? Are you a sound designer looking for ways to evoke a feeling of perpetual motion in your effects? If so, you should really check out the Shepard Tone — an auditory illusion that composers, producers, and sound designers have been taking advantage of for years.

The Shepard Tone defined

The Shepard Tone is an auditory illusion discovered by Roger Shepard, a 20th-century cognitive scientist who worked on many concepts vital to data representation in the modern age. In addition to his fascinating, nerdy output on multidimensional scaling models, he worked out the concepts related to the cyclical aural phenomenon that bears his name. 

The Shepard Tone is a psychoacoustic trick of the mind. The tone itself is just two relatively clear notes played an octave apart: two sine waves separated by an octave is the most basic example of a Shepard Tone.

But when you use this sonic formation in a chromatic scale — either moving up or down — a curious thing happens: you’ll hear pitches that either ascend or descend, but never arrive at any resolution. 

This is called a Shepard Scale, and it’s been likened to the audio equivalent of a barber pole. 

Roger Shepard researched this and other illusions whilst working at Bell Labs, publishing an article entitled “Circularity in Judgments of Relative Pitch” in 1964. It’s within this article that we can trace the earliest known origins of the “Shepard Tone.”

The Shepard Scale explained

Classically defined, the original Shepard Scale consists of two or more sine waves, each played an octave apart, layered together in such a way that one set of sine waves gradually rises in volume, as another set gets softer and softer. 

The result? A powerfully tense phenomenon: the illusion of a continuously ascending pitch, even though it’s essentially a looped phrase.

That loop is actually 4 measures looped 5 times:

It’s hard to know where the splice point is – and that’s what Shepard Tones and Shepard Scales can net you. Our brains are confused by this pattern, and are never able to resolve the ascensions in pitch. The illusion is so powerful that it can evoke a sense of severe dread or unease.

Variations on the Shepard Tone and Shepard Scale

Shepard may have happened upon the tone, but others shepherded it along in various ways. 

One variation on the Shepard tone is the Shepard-Risset glissando, developed by Jean-Claude Risset. 

A Glissando is a seamless, legato slide between various notes, like so:

With that information in tow, you can guess what the Shepard-Risset Glissando is: a seamless, continuous version of Shepard Tone, played not in discrete chromatic intervals, but in one long rising legato. 

In the following example, I’m using the principles behind the Shepard-Risset Glissando while sound-designing a podcast for Voyage Media. While the narrator details a traumatic experience in her childhood, the musical underscoring looks like this:

These automation lanes represent a rise in pitch, staggered in a way that pairs with the natural volume dips in this drone’s waveform, creating a Shepardian effect:

How to make a Shepard Scale in a DAW

Creating a Shepard Scale requires a careful combination of pitch, volume, and timing. Here’s a basic way to do it:

1. Using a simple sine-wave generator, create a MIDI part that goes up chromatically, like so:

2. Duplicate this MIDI part and transpose it either up or down by one octave.

3. Choose one of your MIDI parts, and adjust the velocity of the notes so that they crescendo (increase in volume) from soft to loud. 

4. Choose the other MIDI part, and adjust the velocity of the notes so that they decrescendo (decrease in volume) from loud to soft.

5. Play both parts together, sit back and marvel at the results:

6. Experiment!

Now that you understand the fundamentals, you can begin applying this technique in your productions. Perhaps you’ll use pitch and volume automation in your DAW to create a Shepard-Risset Glissando. Maybe you’ll explore the concepts of Perpetual Melody. Really, the world is your oyster. 

To get you going, here are more examples of Shepard Tones in the real world.

Real-world examples of the Shepard Tone in use

The Shepard Tone is primarily used as a sound design tool in various kinds of media, though occasionally it finds its way into experimental or avant-garde compositions as well. Here are some examples from various forms.

Music production

In music production, the Shepard Tone is often used to build tension or create a climactic moment in a song. You can hear examples of the Shepard Tone as early as 1967, in the ending of “I Am The Walrus.” In this tune, the string parts engage in Shepardian behavior. 

Shepard Tones also make for excellent risers. You can hear it used this way to great effect in the song “Won’t You Be There” by Nero:

Film and television

The Shepard Tone is also widely used in film and television soundtracks. Directors and sound designers use it to evoke a feeling of tension. A notable example is Christopher Nolan's film Dunkirk, where the Shepard Tone was employed to create a continuous sense of rising dread throughout key scenes. 

The tone’s ability to make the audience feel like something is always about to happen, without any actual resolution, heightens the suspense and keeps viewers on the edge of their seats.

That’s the most common example given of the Shepard Tone in film scores, but Nolan has been playing around with them since the Batman times: the sound of the Batpod’s gears shifting is, in essence, a Shepard Tone effect.

Video games

In video games, the Shepard Tone is used to enhance the immersive experience, especially in levels that require heightened tension or alertness. Perhaps the most popular example of this is in Super Mario 64, during the endless stairs sequence:

Add the Shepard Tone to your flock of tricks

Now that you’ve been fully shepherded through the wonders of this glorious effect, we invite you to use the Shepard Tone in your music productions and feats of sound design. To understand more about how psychoacoustic effects work in audio, definitely peruse this article.