La Roux’s volume of Renaissance’s mix album series Sidetracked underscores that Elly Jackson and Ben Langmaid have a clear -- but not simplistic -- aesthetic. It’s not a shock that their mix features plenty of ‘80s synth pop. However, La Roux are among the few ‘80s revivalists that understand that decade’s sounds so well that they embody them instead of just rehashing them. Here, they present some synth pop gems that have a few wrinkles underneath their smooth surfaces: Blancmange’s percolating “What’s Your Problem” and Freur’s “Doot Doot” are quintessential without being ubiquitous. Japan’s version of “I Second That Emotion” -- which channels Roxy Music as much as it does Smokey Robinson -- is a particularly inspired choice, since Jackson’s vocals often reveal more soulful influences than the mechanical sounds that dominate La Roux. However, Langmaid and Jackson’s choices aren’t just a template for their music (although Joyce Sims’ “You Are My All and All,” which blends powerful vocals with tinny electronics, is definitely part of their blueprint). The dark, sparkling disco-funk of Dutch group Fox the Fox’s “Precious Little Diamond” and Gerry Rafferty’s smooth “Right Down the Line” are left-field choices that add more personality to the mix, and Doris Troy’s “Just One Look” is such a stone-cold classic that La Roux didn’t bother remixing or otherwise tampering with it. Not every song here is from the past: La Roux include tracks from their contemporaries, even though those artists are fond of the ‘80s too. The D. Lissivik remix of Fever Ray’s “When I Grow Up” retrofits the track with synth pan-pipes and electro toms that recall that decade's worldbeat craze and trade otherworldliness for cheeky faux-exoticism. I Blame Coco’s bittersweet “Self-Machine” and Kavinsky’s “Testarossa Autodrive (SebastiAn Remix)” also have a decidedly retro feel (Kavinsky has another single named “1986” for a reason). For their own track, however, Langmaid and Jackson go even further back in time to the Rolling Stones’ “Under My Thumb,” yet it’s one of the most modern-sounding songs they’ve recorded. A cohesive mix with just enough twists to make it interesting, this volume of Sidetracked will satisfy pop fans and crate-diggers alike.