When the Bang on a Can mainstay first heard Lou Reed’s Velvet Undergound song, “I just remember being completely terrified. I was danger and terror and drugs and sex. It was twisted and relentless.” 35 years later, Lang has rewritten the piece for voice and cello. (For the same LA Phil program, Michael Gordon has turned Vivaldi post-minimalist, and Julia Wolfe has made the drum set Stravinskian.)