Whether you consider her a peddler of precious, pretentious twaddle or an endless font of pure Icelandic genius, you have to give Björk credit for eschewing the safe option. No other platinum-selling diva has had the guts to forge such idiosyncratic paths as this charismatic singer has done over the last 11 years. Now, on her sixth post-Sugarcubes studio album, Björk reminds us that the voice -- hers, those of Robert Wyatt, Mike Patton, London and Icelandic choirs, and others -- is infinitely malleable and fuckin' weird, dude. Furthermore, its arsenal of sounds is as rich as the most loaded software program, as this all-a cappella album proves. Medulla sounds both ancient and avant-garde, hauntingly beautiful and fascinatingly repulsive. Bolstered by pliable beatboxing from the Roots' Rahzel -- plus subtle production tweaks and brilliant arrangements from Mark Bell, Valgeir Sigurdsson, and Björk herself -- Medulla is her most compulsively listenable album, and her most challenging.