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Starting with the parenthetical title, obscurity seems to be the sole objective on the third album from Iceland’s Sigur Rós. The eight lengthy tracks — 71 minutes in all — come without names; and to top it off, ethereal vocalist Jón Pór Birgisson croons in a made-up nonsense language called Hopelandic. But don’t be put off by the gimmicky trappings. The quartet’s elegant compositions have a haunting symphonic sweep, echoing the best of ’70s progressive rock. Songs unfold slowly and deliberately, with melodic repetition building tension as layers of sound accumulate. A few soothing notes aside, the result is a sense of creeping anxiety that suggests a soundtrack for a David Lynch film. Subtle, spooky — perfect for 2 a.m.