There's a good reason that most rock bands aren't duos—the sonic palette dries up quickly. Blues-rock tandem The Black Keys appeared to max out its potential on 2004's Rubber Factory, eschewing the primitivism of its previous releases and embracing full-bodied arena-rock stomp. At that point, The Black Keys should have hired a bassist, a second guitarist, and a boogie-woogie keyboardist and become this generation's Bad Company. Instead, The Black Keys tapped producer Danger Mouse to bring some sonic variety to Attack & Release, a tacit admission that the two-man blooze formula had finally worn thin on 2006's samey Magic Potion. So what does a Danger Mouse and Black Keys collaboration sound like? At its best, it sounds like "Psychotic Girl," which pares the band's usual riff-heavy bluster down to a slinky guitar, sleepy drums, and Dan Auerbach's lustful moaning, and lays it on a bed of disembodied voices and psychedelic banjo plunking. Here, Danger Mouse helps deconstruct and reassemble The Black Keys into something fresher than the sum of their overly familiar parts. Attack & Release falters on the rockers, which sound like the same old Keys, for better or worse. But when Danger Mouse coaxes out the band's soul side on the slow 'n' sexy "All You Ever Wanted," The Black Keys suddenly find a way around their self-imposed restrictions.