I finally got around to watching Dunkirk today. It’s stressful. But it’s beautifully made, and there was a variation on Elgar’s ‘Nimrod‘.* Which mostly drove me crazy by pretending to be Nimrod, very slowly, for a bar or two, without ever becoming Nimrod. In looking it up later, I learned that it wasn’t actually Nimrod, which mostly exonerated it.**
Anyway, one of the way that your blood pressure gets ratcheted up in this film is the Shepard tone. Identified by cognitive scientist Roger Shepard, the Shepard tone is an auditory illusion that gives the listener the sense of a perpetually rising tone without ever actually rising. Using overlapping tones, as the scale rises the top end fades out and allows the bottom tone to pick back up very quietly as the other pitches continue to rise. It’s sort of like a round of, say, Frere Jacques, where after you’ve finished the line “ding dang dong”, you pick back up at the top of the round with “Frere Jacques” while your friend moves into the “ding dang dong” line. While this is happening, you’re quieter in the initial “Frere Jacques” and the ultimate “ding dang dong” lines, and louder in the middle “dormez-vous” and “sonnez les matines” lines. The Shepard tone is a more uniform and linear version of this idea that tricks your brain into thinking it’s continually climbing. The effect of that is a sense of mounting tension, and Dunkirk‘s composer, Hans Zimmer, uses this masterfully. You can hear it (and the snippets of Elgar) in this piece.
To hear what a Shepard tone sounds like in isolation, listen here.
For more on the theory of the Shepard tone from some BBC scientist types, see here.
**It is, however, a brilliant choice of music for people familiar with the wave of Elgar’s (posthumous — he died in 1934) popularity in England at the time.