doubly titled (it translates loosely as'haven-home') sigur rós's new album is a record of two halves. the hvarf half (do keep up at the back) is a five-track collection of mostly unreleased rarities from the group's archives, while heim features six-acoustic reworkings of back catalogue favourites. of the outtakes, salka pulls off the profoundly icelandic trick of sounding both despairingly melancholy and utterly life-affirming, while hijomalind -all ice-floe keyboards and soaring, imperious guitar chords etched with jonsi birgisson's schoolboy falsetto - is perhaps the quintessential sigur rós song. the acoustic remakes are no less persuasive. von, the title track of the band's 1997 debut album, gets an especially beauteous reworking courtesy of string quartet amiina's melancholy threnody and a rudimentary tom-tom part. whatever is behind sigur ros's ineffable nordic magic, it doesn't appear to be powered by electricity.