Tuning in to a music-as-redemptive-force frequency, black-and-white documentary Music From the Big House follows Canadian roots musician Rita Chiarelli as she collaborates with inmates at Angola, the plantation turned maximum security prison in east central Louisiana. An informal historian of the blues with a formidable rasp of her own, Chiarelli hopes that by uncovering the "new music from behind those walls" and presenting it at a big-event concert in the state pen's chapel, she will extend the jail's long musical tradition. (Lead Belly was pardoned and released after performing for the governor there in the 1920s.) Though much of the movie is about the particular catharsis afforded by country, blues, and gospel, the soundtrack's recurrent tone-setter is the weightless first track from Brian Eno's Music for Airports, used to emphasize the inmates' long-haul coming to terms with both confinement and the transgressions that led to it. This personal-journey material, which eventually eclipses the mildly rousing concert footage, ultimately feels a bit thin-- Chiarelli interviews the prisoners about their big-picture views on hope, guilt, and forgiveness, but the charges that landed the men behind bars are listed only in a pre-credit postscript. Director Bruce McDonald, maker of the intriguing narrative features The Tracey Fragments and Pontypool, has assembled a strikingly shot film with impressive prison-grounds access and a basically unimpeachable power-of-music message, but it finally feels too cautious, as if digging a little deeper might compromise the prevailing tone of tentative uplift.