Some might expect that after Björk's recent underwhelming minimalist excursions, she'd give up the glitchy dabbling and make a triumphant return to more song-like structures. Not quite. While Volta features a couple of stripped-down lullabies that find her softly whispering over what sounds like a koto recorded underwater, they seem less like fully realized ideas than rough demo sketches. That's true of even the more elaborately orchestrated pieces here, like crunching opening march Earth Intruders. It's like Björk is still playing with the conventions of harmony, melody and rhythm but hasn't yet decided exactly what to do, so in the meantime she's issued an unconnected collection of new experiments as a progress report. Fans might find it a fascinating revelation, and Madonna will likely swipe a few ideas, while everyone else is left wondering what happened to the tunes.