“Don’t ask me why/Why there is sorrow,” Frankie Rose sighs on the opening line of “Sorrow.” The singer/songwriter may not have any answers in the lyrics of her new single, but the former Vivian Girls member decisively doubles down on the dream-pop of 2012 album “Interstellar” and strays even further away from the garage-rock sound of her previous musical outfit. “Sorrow” is lighter than even the airiest “Interstellar” tracks, with the chorus yielding a descending “Why-y-y” refrain that’s deceptively simple and wholly impossible to resist. The back half of the song also presents some unexpected sonic treats, including a string arrangement that bulks up the track’s emotional impact and a roaring outro that rewards patience. Along with all of its positive qualities, the first single from “Herein Wild” mesmerizes due to Rose’s feathery voice carefully dipping into each syllable. Even with lesser arrangements, the singer’s delivery is irresistible.