As a farewell to a century of musical innovation, Sonic Youth devote a double album to covering legendary avant-garde recordings such as John Cage's "Six," James Tenney's "Having Never Written a Note for Percussion," and Christian Wolff's "Edges." As a further token of gratitude, Sonic Youth had other avant-garde musicians such as William Winant collaborate with them on these covers. The result is a minimal album of silence occasionally interrupted by strange dissonance that quietly reaps noisy havoc on your mind. The many collaborators make Goodbye 20th Century a curious listen -- certainly not your standard Sonic Youth album. Actually, it's not too far removed from the other SYR EPs, especially in terms of production sound. But anyone looking for standard fare here is going to be greatly disappointed. These aren't songs -- they're compositions and they're performed as such. Alt-rock this is not.