Few artists define "experimental" quite as effectively as Björk, which goes a long ways towards explaining how she has managed to remain so relevant throughout her three-decade career. It also adds weight to the claim that Biophilia, her eighth full-length, is her most experimental to date. There's the ambitious plan to set up apps for each track in which the users can manipulate the music, and each song's thematic focus on juxtaposing various physical and musical properties (lighting/arpeggios, gravity/counterpoint). But the most jarring feature of Biophilia is the sound, or perhaps more appropriately the lack thereof. Opener "Moon" does a fine job of setting the tone; nothing more than a lone harp set against Bjork's voice for the its nearly six-minute runtime. This framework — sparse arrangement, led by unorthodox instrumentation (xylophone, church organ, tesla coil, something called a "gameleste") — is largely repeated through the album's 10 tracks, and initially, can feel more than a little jarring. However, Biophilia's not-so-secret weapon is Björk's voice, which, left out in the open, only gains potency and purpose. Though the relentless experimentation can seem overwrought, particularly in the lyrical content, Biophilia is another welcome step forward for music's most restless artist.