“To me, the vocals are more important than guitar playing — or anything, really,” Polly Jean Harvey told Rolling Stone in 1993. She meant it: Harvey’s vocal approach has changed tack many times over the years, and every time, it’s striking. The rocking roar of Dry and Rid of Me, her first two albums, in 1992 and 1993, bent toward blues with To Bring You My Love in 1995, went toward a lighter, airier, clearer voice on White Chalk in 2007, adding a near-Broadway breadth and depth for Let England Shake in 2011. The opera lessons she began mid-career helped. But they were merely icing on a voice that was commanding from jump.