Christopher Nolan explains the 'audio illusion' that created the unique music in 'Dunkirk'

Christopher Nolan has never been shy about challenging audiences with unique musical scores in his movies.

For 2010's "Inception," composer Hans Zimmer took Nolan's reference in the script to Edith Piaf's song "Non, je ne regrette rien," and slowed it down to create one of the major musical themes of the movie. Then Zimmer and Nolan's collaboration for 2014's "Interstellar" led to the movie's powerfully haunting organ music. 

Nolan is constantly thinking about the music for his films at the script stage, and his latest, "Dunkirk," is no different.

"Very early on I sent Hans a recording that I made of a watch that I own, with a particularly insistent ticking, and we started to build the track out of that sound. And then working from that sound, we built the music as we built the picture cut," Nolan told Business Insider.

But the score went beyond having just a ticking theme for the story, which tells three different timelines surrounding the evacuation of Allied forces from Dunkirk, France. To build the drama of those three stories coming together for the movie's dramatic conclusion, Nolan went back to a musical technique he played with in one of his early movies.

"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," Nolan said. "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. So 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."

Perhaps what makes this score by Zimmer the most powerful out of his Nolan projects (a collaboration that goes back to "The Dark Knight" franchise) is the limited amount of dialogue in "Dunkirk." Zimmer's ticking score doesn't just heighten the thrills, but explains what's going on in the scene as much as the photography does.

Listen to a portion of the "Dunkirk" score below: