Over the years, Iceland’s Múm has undergone a few personnel changes as well as stylistic shifts. On its sixth studio LP, the group successfully unites its experimental side and its pop side, though the acoustic, folk-inflected timbre of Sing Along to Songs You Don’t Know has vanished. Múm now favors a more electronic environment—one that sounds in many ways like the band's early work. Muted percussive bits beat like hummingbird hearts under otherwise glacial and crystalline compositions, with willowy violins and echoing pianos feeling both stark and rich. Layering glitchy blips with static-wrapped vibrations and plinky pianos is the easy part; it’s making those elements work with the grace of Múm’s classical components and its eerily beautiful vocals that’s tricky. “Underwater Snow” goes from delicate to bracing, with ethereal, arcing harmonies that rise and fall like … snow; the piece is hair-raising, in the best of ways. Original member and vocalist Gyða Valtýsdóttir returns here after a 10-year hiatus, which may be one reason Smilewound has the vibe of early Múm, while sounding all growed up at the same time.