Watch: How 'Dunkirk' Uses a Classic Audio Illusion to Ratchet Up the Tension
The auditory phenomenon known as the Shepard tone is used to add suspense to Dunkirk.
When filmmakers use every cinematic element at their disposal, good films can become great, and this isn't just the case for big-budget blockbusters. One filmmaker who has had an intuitive understanding of this principle from his first film is Christopher Nolan, whose current blockbuster Dunkirk uses visuals, music, and even sound itself to shape its story, in the form of the auditory illusion known as the Shepard tone.
Composer Hans Zimmer and Nolan have enjoyed a fruitful collaboration; their work on Inception made use of one song, manipulated, as a way to link the various pieces of the film, and Interstellar featured a haunting organ score, also by Zimmer. Like many directors, Nolan has an idea of the music and sounds he wants to use long before the start of production. While writing Dunkirk, he began to focus early on the ticking of a watch that he owned: Taping the sound, he sent it to Zimmer, and together, they used this ticking to build out the score and add tension to the film's three interwoven storylines.
Shepard tones can be hidden inside of a film's sound design to cause effects in an audience that they're not even aware of.
But that's not all. The two also revisited a technique first used by Nolan in 2006's The Prestige (where he worked worked with composer David Julyan.) Known as the Shepard tone, it's an auditory illusion, known for hundreds of years, that consists of "several tones separated by an octave, layered on top of each other." The technique has been used in everything from Bach's Canon, to the Beatles' "I Am The Walrus," and even Mario 64. According to Vox's video, as "the tones move up the scale, the highest-pitched tone gets quieter, the middle pitch remains loud, and the lowest bass pitch starts to become audible." But talking about music, as they say, can be like dancing about architecture, so it's probably better to let you listen:
Nolan wanted to use these tones to link the stories, to "...build the music on...mathematical principals...there's a fusion of music and sound effects and picture that we've never been able to achieve before.” While the tones seem to be getting higher (they can also seem to descend, of course), in fact they never do, and the effect is capable, if used in a specific way of producing, "anxiety and panic attacks."
Carefully modulated, Shepard tones can be hidden inside of a film's sound design, much like the infrasound effect I wrote about last month, to cause effects in an audience that they're not even aware of. That being said, Zimmer and Nolan are not trying fool anyone or send them screaming from the theater.
Interested in experimenting? This technique is by no means beyond the reach of the indie filmmaker. This tutorial shows how any DAW (digital audio workstation) is capable of producing the effect, so check it out and see what you can come up with. You can even generate your own tones here with the caveat to exercise caution, particularly if you're susceptible to panic attacks. Basically, just try not to freak yourself (or anyone else) out.