Múm defined their approach -- twinkling electronics, wispy vocals, acoustic instrumentation here and there -- so clearly on their first few albums that the rest of the collective's work often seemed caught between staying in place and branching out.

They do a little of each on Smilewound, which marks the return of founding member Gyða Valtýsdóttir, one half of the twin vocalists who helped craft Múm's signature sound.

Adding her to the fold again allows the group to revisit the pastoral folktronica of yore, most potently on "Slow Down," a half-speed chase so delicate it sounds in danger of floating away before it can reach listeners' ears.

Meanwhile, Hildur Guðnadóttir -- who joined the band with 2007's Go Go Smear the Poison Ivy -- represents the more dynamic, experimental approach of the collective's later work on standouts like the sprightly 8 bit-synth-driven workout "When Girls Collide" or the drum'n'bass-tinged "The Colorful Stabwound." Ideally, these sounds should balance each other, but too often switching from style to style makes Smilewound unfocused.

As on Go Go Smear the Poison Ivy and Sing Along to Songs You Don't Know, having multiple vocalists makes for a fragmented listening experience, and tracks like the drifting "Eternity Is the Wait Between Breaths" feel aimless on an album that already needs more direction.

Thematically, Múm return to contrasting innocence and danger, and the results -- as with many things on this album -- are mixed.

"Underwater Snow" pits cozily twinkling pianos against rumbling beats in a way that suggests breaking a snowglobe; "Time to Scream and Shout," a perversely whispered lullaby of destruction, feels almost like a parody of their approach.

However, Múm make up for it with "Candlestick," Smilewound's most exciting song and one of their most potent mixes of sweetness and violence yet.

Over brisk synth-pop, Guðnadóttir flirts by threatening to smash her beloved with the titular blunt object before deciding "I kind of like your face the way it is." It's even catchier than "Whistle," the group's collaboration with pop queen Kylie Minogue, which closes the album with a pretty, if not thrilling, slice of their signature sound.

Smilewound is all over the place; Múm are doing a lot, and doing some of it well, but they never bring it together in a coherent statement.