Strictly speaking, this isn't a Lambchop gig. In 2003, during the writing of twin albums Aw C'mon and No You C'mon, the sprawling alt-country band performed a live score to FW Murnau's 1927 silent movie Sunrise at the San Francisco film festival. This evening they repeat the performance. As the film is screened, the eight musicians that make up Lambchop's core are in a line with their faces to the screen and their backs to the audience. You can occasionally see a flash of movement in the dark but that, visually, is that.

In many ways, it's the perfect arrangement for a band who have never been known for their dynamic stage presence or affection for the spotlight. Sunrise, meanwhile, has aged well. Its tale of a city girl who seeks to trick a poor farmer into killing his wife and selling his farm is both high on melodrama and parable-like in its simplicity, but its mixture of menace and exuberant slapstick is entrancing.

Lambchop are even sparser and more careful than usual. Frontman Kurt Wagner's voice breaks occasionally over their charming mix of country, soul and indie-like Morse code: you note its absence or its eerie presence, but can rarely tell what he's singing. Yet for all its restraint, this is still a busy soundtrack, and one that often seems to work against the action on screen. At one point the protagonist is rowing frantically, his face a picture of anguish, while the band play an easy, lilting rhythm.

Ultimately, for all its moments of rootsy beauty, Lambchop's soundtrack seems caught between two poles: it is neither vigorous enough to dominate the movie, nor retiring enough to simply complement the action. Often, it blurs into a pleasant sonic smudge, illuminating the film in a dim light. The effect is atmospheric, but hardly mind-blowing.

· At the Philharmonic Hall, Liverpool (0151-709 3789), tonight, and at the Barbican, London EC2 (020-7638 8891), tomorrow.