“Choirgirl” is something of an empty descriptor, but maybe that’s why it fits for the voices of identical twins Alejandra and Claudia Deheza: They sing with a kind of crisp breathiness, delivering lyrics in a clear tone that’s as mannered as it is lovely. They’re plenty talented, but their talents don’t make School Of Seven Bells essential. As on 2008’s similarly sleepy Alpinisims, Benjamin Curtis of Secret Machines pairs their voices with precisely arranged but relentlessly conventional post-shoegaze, post-trip-hop dream-rock. “Dust Devil” demonstrates the conundrum at the heart of this band: While it marries cool-sounding, hard, almost-club-ready synth blips with the Dehezas’ placid harmonizing, it doesn’t offer anything to overcome the fact that electro beats bolstering haunting female vocals have become cliché. “Windstorm” boasts a hook that people might remember later, and “Dial” stands out by escalating with foamier and foamier Spiritualized-style plateaus, but even those tracks provide only superficial satisfaction. The lyrics never step beyond New Agey, four-elements platitudes, and the arrangements, even when ostensibly dark, never cut against the vocals’ immaculateness. If only someone would occasionally flub a note, just for the sake of a specific, discernable emotion.