For punk, metal, or hard rock bands, the unplugged album is the one that shows whether they've been succeeding simply on energy and volume or because of real talent.

(Anyone who remained a skeptic of Kurt Cobain's songwriting skills must have been converted by Nirvana's MTV Unplugged masterpiece.) And Octahedron, a quieter and more subdued Mars Volta album, proves that same fact (if not at the same level as Nirvana) for a band that's perpetually lived on a knife's edge of tension.

Recorded in less than a month, Octahedron is by no means an unplugged album -- it's not acoustic, it's not confined to ballads, and it includes consecutive hard rockers in "Cotopaxi" and "Desperate Graves" -- but it charts a different direction for the Mars Volta, and proves they don't need to shuttle between dynamic extremes in order to succeed on an artistic level.

The format allows a greater role and more space for John Frusciante, who accompanies Cedric Bixler-Zavala's vocals well, and also provides his own highlights, channeling the Edge on the emotional "Teflon" and, later, echoing Pink Floyd on "With Twilight as My Guide." With a few exceptions, Zavala's lyrics are as arcane as ever; the glossary for "Halo of Nembutals" alone would include the words "vermin," "sloth," "ringworms," "necrophiliacs," "carcinogen," "asp," "communion-shaped," and "palindromes." Still, they achieve scrutability far more often than in the past, and reveal more of the tenderness that was occasionally visible in Mars Volta material.

("Since We've Been Wrong," the single and first track, is especially affecting.) Calling this an unplugged album is useful only in relation to what the group has produced in the past, but what the Mars Volta created on Octahedron will provide them with more range and opportunities in the future.