Don't take the title of Mumford & Sons' fourth album literally: maybe it's named after the birthplace of the blues, but Delta doesn't have much to do with American roots music of any kind. Working with producer Paul Epworth -- a Grammy winner for his work with Adele who also helmed efforts by U2 and Rihanna -- Mumford & Sons pick up where Wilder Mind left off, choosing to expand that 2015 album's glossy adult alternative instead of abandoning its refined aesthetic. The twist Epworth introduced lay entirely in the studio. He had the band bring in their trademark acoustics but treated these old-fashioned instruments with a host of digital effects, so they rarely sounded like a guitar and banjos. Perhaps this had a liberating effect on Mumford & Sons, allowing them to jam and create in ways both familiar and new, but it's hard to hear a kinetic spark on Delta. Rather, it's a measured and subdued affair, proceeding at a deliberate pace and unfurling at a hushed volume; even at its loudest moments, it seems quiet, even muffled. This kind of well-manicured production, when paired with a series of songs focused on internal journeys, ultimately has a lulling effect. There is a pulse, but it's soft and turned electronic. There is emotion, but it's been intentionally encased in a digital cocoon, one that flattens the group's bold accents (such as an embrace of vocoders) and turns Delta into soft, shimmering background music, ideal for any soothing setting you'd like. ~ Stephen Thomas Erlewine