Outgrowing the wild-hearted club anthems that defined her ascent, Kesha sounds reborn on her third album, commanding a set of sonically broad, heartfelt pop. Here, she punctuates the assertive funk of “Woman” with The Dap-Kings’ horn section and sings country-touched harmonies with Dolly Parton. But Rainbow is held together by Kesha’s elastic, giggle-to-roar vocal, which sounds best on blasting, jittery confections like “Boogie Feet” and “Learn to Let Go."