“Youth,” the first feature film by Paolo Sorrentino since his Academy Award-winning ode to Rome, “The Great Beauty,” stars Michael Caine as Fred Ballinger, an aging composer passing time at an Alpine resort and reflecting on his life. Much of the drama hinges on whether he will conduct a concert of a work that made him famous, his “Simple Song #3,” inextricably linked in his mind to an irrecoverable past.
To score the film — and to write “Simple Song #3” — Mr. Sorrentino turned to David Lang, the celebrated new-music composer, based in New York, whose work has been described as post-Minimalist.
When Mr. Sorrentino started on “Youth,” which opens in the United States on Friday, he immediately thought of Mr. Lang. “He’s able to create music that’s very complex, but also music that’s very accessible while remaining refined and intelligent,” Mr. Sorrentino said by phone. “He seemed the best contemporary composer to do the soundtrack.”
Usually, scores are written after the filming, when the editing is underway. For “Youth,” Mr. Lang, 58, had to finish before the filming began, since the refrains of melody are an important plot point. Fragments of “Simple Song” are played by different figures: a young boy practicing his violin, and the virtuoso violinist Viktoria Mullova and the soprano Sumi Jo, who perform the work with the BBC Concert Orchestra on screen and on the soundtrack.
For several months, he and Mr. Sorrentino were in long-distance communication. “I kept sending demos of the song to Paolo, things that I thought were emotionally devastating,” Mr. Lang said. “He would write back and he’d say, ‘I’m sorry, I am crying a little, but I need to cry a lot.’”
The breakthrough eventually came. “There’s this gigantic crescendo to a big explosion toward the end of ‘Simple Song,’ where the whole orchestra comes in and it’s really loud,” Mr. Lang said. “In my first version, the whole orchestra comes in, but it wasn’t really loud, because I just thought, I don’t want to be so demonstrative.”
“When I sent him the last demo,” Mr. Lang said, “all he said was, ‘David, now I am crying.’ And then I knew I had it.” He said he was grateful to Mr. Sorrentino for pushing him into new territory.