Revered for their ineffably clean, precise playing, Tortoise couldn’t help but mess with the formula slightly on their fourth album, Standards. And from the beginning of the first track it sounds like a major overhaul, with heavily over-miced drums and distorted guitars framing a pummeling groove from bassist Doug McCombs. On the second track “Eros,” the phlegmatic synthesizer lines and clipped drums are more reminiscent of experimental electronica outfit Mouse on Mars than any fellow post-rock luminaries. When the band finally hits its stride, though, midway through the third track, “Benway,” it’s with a quintessential Tortoise groove, driven by repetitive bass figures and a vibraphone melody (plus a hilarious nod to prog-rock at the end, with several seconds of stop-start playing). Standards does return the group to the green fields of their last record, but only occasionally; John McEntire and company appear too restless to consider making the same album twice. Ironically, despite the range of sounds, Tortoise is still doing what they’ve been doing for nearly a decade: playing some of the most empathic, group-minded rock of their era, then indulging in much recomposition courtesy of the mixing desk and various effects. “Monica” is one of the least Tortoise-sounding tracks the group has ever recorded; it sounds like an early-’80s pop/R&B track (complete with talkbox guitar) filtered through the lens of British IDM, but then mutates into an intriguing stereo-separation drum workout. Overall, Standards has a few detours for fans conscious of any band’s “progression,” but plenty of interesting songs and great musicianship for less vested listeners. Though it doesn’t develop the evocative or impressionistic side of Tortoise (as heard on TNT), the band is certainly as inventive as ever. – John Bush