Don’t let their spot as Jimmy Fallon’s house band fool you — The Roots haven’t softened one bit. Their latest release is a concept album about a youth drawn into street life until it results in his death, told in reverse. Despite all the inherent bleakness that would imply, lyrically, musically Undun is not so dour, buoyed by vibrant soul and touched by flourishes both electronic and orchestral that suggest how far the Roots have come as a band and as conductors of a sound they alone seem to inhabit. The sumptuous “Make My” calls to mind the ambitious soul of Stevie Wonder, Curtis Mayfield and Marvin Gaye, while the fluid and funky “Kool On” displays the band’s subtle musical chops while giving some of its most spirited rhymes. And “Lighthouse” takes its “face down in the ocean” metaphor to moving heights and could — gasp — sit comfortably on pop and hip-hop radio without even trying for that specifically. After its jazzy interludes close out the album, including an instrumental by Sufjan Stevens, you may want to spin the terse Undun again and again, both to unravel its conceit and to enjoy its musicality.