sigur rós' fifth album is the icelandic band's most worldly, varied and — considering the usual ice-floe speed of their rock — impetuous. co-produced with flood (depeche mode, u2), the record was made quickly — mostly in new york and london, with a trip to havana for some vocals — and it opens with the closest this group will ever come to boogie-woogie: "gobbledigook," a cheerful tumble of acoustic guitar and drum-circle percussion. the album also features singer-guitarist jónsi birgisson's first venture into english-language whisper and falsetto, the closing piano-and-brass suspense of "all alright." but what happens between those two songs is the real leap forward. having mastered a uniform majesty on 2002's ( ) and 2005's takk . . . , the band achieves a new unity in variety here, winding from near-glam romp and fireside-folk warmth to slow-climb grandeur with an attention to the repeated payoff in a sturdy hook and hum-along chorus. sigur rós titled an early spook-rock epic "popplagid" — icelandic for "the pop song." now they are actually writing them.