The Black Keys’ sixth album, Brothers, gets off to such a weird start that it’s remarkable the record rallies as strongly as it does. The grubby disco beat and trembling falsetto of opener “Everlasting Light” is so off-model that it almost seems designed to scare longtime fans away, and the song that follows, “Next Girl,” runs the duo’s riff-heavy rock through so many filters that it loses almost all of its visceral impact. But those kinds of swings and misses are all part of The Black Keys’ evolution. Over the past few years, guitarist Dan Auerbach and drummer Patrick Carney have looked for ways to contemporize, after taking their two-piece roadhouse-blues act about as far as it could go on their 2004 classic Rubber Factory. Brothers is fully committed to the visionary hybrid of the archaic and modern that The Black Keys have only tentatively attempted before. Whether it’s the cheery whistling and robotic drum fills of “Tighten Up” or the rubbery, synthetic snap of “Howlin’ For You,” Brothers is actively engaged in exploring how to make beloved old sounds relevant to now, and the result is that even classic Black Keys howlers like “Black Mud” and “Ten Cent Pistol” come off more vital in the new context. Before, The Black Keys made the kind of music that crate-diggers might sample. Now they sound like they’re sampling themselves.