The Black Keys’ sonic evolution over the past several years was both inevitable and necessary: There are only so many combinations Dan Auerbach and Patrick Carney could have wrung out of the two-man scuzz-blues minimalism of their first four records. Thus began a fruitful relationship with Bryan ”Danger Mouse” Burton, who has co-produced every Keys outing since 2008’s Attack & Release. The band’s eighth album, Turn Blue, bears perhaps his biggest thumbprint. Auerbach and Carney have toyed with psychedelia, but Blue sounds more like an extension of Burton’s Broken Bells side project with Shins frontman James Mercer than the follow-up to the Keys’ muscular, arena-ready 2011 best-seller, El Camino. Blue opener ”Weight of Love” is a nearly seven-minute dynamo with chemical assistance from drowsy organ hums and plenty of Claptonized soloing. The rest of the record glides through that same intergalactic place; it’s meticulously executed but slightly (and sleepily) monochromatic. Their roots only emerge fully on closer ”Gotta Get Away,” an acid-tongued, uptempo slide-guitar stomp. As a sop to longtime fans, the song provides reassurance that no matter how far out their space explorations take them, they’ve always got one foot in the gutter. B+