Combining no-wave din with a fondness for classic rock, Sonic Youth laid the groundwork for some of the biggest alt-rock bands of the '90s. They helped Nirvana get signed to a major and paved the way for mixed-gender bands like Hole and Blonde Redhead. And their inventive tunings and all-encompassing feedback swirl trickled down into noisy acts like Unwound, My Bloody Valentine, Liars, and beyond.