Philadelphia’s The War on Drugs, the vehicle of Adam Granduciel — frontman, rambler, shaman, pied piper guitarist and apparent arranger-extraordinaire, returns with Slave Ambient. On their debut, the life-affirming Wagonwheel Blues, and the follow-up EP, Future Weather, The War on Drugs seemed obsessed with disparate ideas, with building uncompromised rock monuments from pieces that may have seemed like odd pairs. Folk-rock marathons come damaged by drum machines. Electronic and instrumental reprises precede songs they’ve yet to play, and Dr. Seuss becomes lyrical motivation for bold futuristic visions. Now, Granduciel has done it again, better than before: Slave Ambient, their proper second album, is a brilliant 47-minute sprawl of rock ’n’ roll, conceptualized with a sense of adventure and captured with seasons of bravado.