The first time I saw the Black Keys live was in 2004, when the band had a very simple blues rock feel. The Akron-based duo was only three albums deep in its discography, with little variation in style across the board.

Guitarist Dan Auerbach and drummer Patrick Carney have since put out three more studio records. “Attack & Release,” from 2008, was produced by Gnarls Barkley’s Danger Mouse, who helped the band expand beyond the basic guitar and drums shtick.

“Brothers,” the latest full-length, not only comes with playful album art, but maintains the level of Danger Mouse’s flashy production.

The Keys have stepped in a new direction. It’s just not possible to play these songs live without more than two members — which is quite a detachment from most of the group’s previous work.

Bass, keyboards and other instruments have never been a prominent part of the duo’s sound. Amongst others, “I’m Not The One” puts this statement to rest with a busy bass line, Beatles-style organ and a subtle string section.

Opener “Everlasting Light” captures Auerbach in a rare falsetto, clearly stating he’s all right with scoping out slightly unfamiliar territory. This rings true to the end, as closer “These Days” is slower and sleepier than any of the band’s other work.

Six years ago, I had no expectation that the Black Keys would become so diverse. Rather than a turn for the worse, their expansion is more likely a sign of the times.