Writing the music for “Rabbit Hole” should have been difficult. The movie — a wrenching adaptation of David Lindsay-Abaire’s Pulitzer Prize-winning play starring Nicole Kidman — details the struggles of a couple coping with life after the sudden death of their 4-year-old son.

Yet composer Anton Sanko wasn’t daunted, perhaps because of the close rapport he achieved with the film’s director, John Cameron Mitchell — he of “Hedwig and the Angry Inch” and “Shortbus” fame.

The key was to avoid the obvious, to make sure the music eschewed push-button tears. “John didn’t want overstatement of the emotional subtext,” Sanko says. “So horns and brass were not going to make it in this kind of movie. His direction throughout was to keep it simple and almost cautiously optimistic. One step over into maudlin meant dire consequences. At the very least it was to be avoided.”

The helmer’s interest in, and experience with, music made the partnership especially rewarding for Sanko. “John is very specific,” the composer says. “And since he knows so much about music, we spent a lot of time going over the score. We even went over the voicing of chords. Most of it was editing down what I had written — keeping it as spare as possible while conveying what was necessary. And John wanted minimal vibrato.”

To accomplish his task, Sanko turned to the tiple, a small stringed instrument in the guitar family that the composer likens to a ukulele. Though mostly associated with Spanish- and Portuguese-speaking countries, the tiple he used was manufactured in the U.S. by Martin guitars and then rebuilt some 20 years ago.

“I didn’t want to get too big, and I wanted the audience to know that it was okay to laugh at certain points, that it was not going to be an intense drama throughout,” Sanko explains, noting how the tiple’s light timbre and bittersweet character suited the film. “I’d be lost without it.”

The score also uses more familiar instruments — clarinets, flute, classical guitar, piano and string quartet — many of which are played by Sanko and his assistant. “I wanted it to be small yet important, and these are the instruments I thought could achieve that,” he says. “I didn’t want the score to be in the way.”

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Michael Brook | Carter Burwell | Danny Elfman | Grizzly Bear | Jan Kaczmarek | Rachel Portman | Anton Sanko