Joni Mitchell has always been a rule-breaker, even as the queen of the ’70s folk-rock scene. Few of her singer-songwriter peers have explored as many emotional moods, offered lyrics of such startling depth or taken so many musical chances. She’s smuggled poignant social commentary into breezy pop tunes (“Big Yellow Taxi”), penned fractured poetry that still ached with emotion (“Coyote”) and abandoned her acoustic roots for kaleidoscopic jazz fusion (“The Hissing of Summer Lawns”). And whether she’s singing about raw need, joyous connection or fathomless loss, Mitchell’s voice remains a thing of remarkable beauty, swinging between fragility and fierceness.