Pop music and classical music are supposed to be different worlds. Yet, in the last few years, the two have begun bleeding together again. On “Colouring of Pigeons,” from Swedish pop duo the Knife’s just-released album Tomorrow, In a Year, one can hear echoes of both Varèse’s Ionisation and Guillaume Dufay floating among metallic passages reminiscent of Björk. The album itself is the score to an opera about Charles Darwin, made in collaboration with avant-garde Berliner Mt. Sims and the British multimedia artist Planningtorock. It merges the artiness of musique concrète and minimalism with the grit of house music.