Max Richter is the genre-defying composer who works for movies, TV, theatre and the concert hall. This documentary by Natalie Johns is about what many consider his magnum opus: Sleep, from 2015 – an eight-and-a-half-hour composition with 204 movements in a plangent, ambient and mellow vein, featuring strings, synthesisers and a soprano, designed to be listened to while you are asleep.

Richter has staged many spectacular overnight performances in venues where audiences are provided with camp-beds, and this film focuses on an open-air event in the Grand Park in Los Angeles. Audiences were invited to fall asleep, stay awake, tune in, tune out, and – presumably – traipse back and forth to the loos at 4am.

This toweringly quixotic work is Richter’s rebuke to the frantic pace of our modern age (which is itself, arguably a form of anaesthesia), although he confesses that it cost him sleep: it was a supremely uncommercial project that had to be worked on at night, after a full day’s work on the movie music that paid the bills.

It is a beguiling film, perhaps because Richter’s work is beguiling. However, it cheats a bit in showing the LA performance; the music we’re hearing appears to come from the studio, not live, something that hits you when you a notice a delivery truck with flashing lights glide in eerie silence behind the orchestra.

So, is Sleep any better or different from the thousands of hours of chill-out music being provided by DJs all over the world? Well, it’s up to audiences to decide. I was reminded of a showing of Andy Warhol’s five-and-a-half-hour film Sleep, from 1964 – simply showing a man asleep – during which a member of the audience stormed up to the screen and shouted: “Wake up!”

• Sleep is in cinemas and available on digital platforms from 11 September.