A Joni Mitchell fan I know -- that is, a woman who exclaimed in a recent e-mail that Mitchell is "everything" -- described the heartbreaking new take of her song "A Case of You" on Both Sides Now as "profoundly sad." It's tempting to label any song set atop a gloomy string arrangement as sad, but "A Case of You," like all of Mitchell's best songs, emerged from deep furrows; conductor Vince Mendoza's arrangement isn't just a black tie slapped on a melancholy folk scarecrow. Mitchell's voice has deepened and wrinkled, but she isn't melody-challenged like, say, Marianne Faithful, who also has a dark saloon album out. She sings from the shadows, wizened like the Sinatra of the early 1960s, but refuses to wallow in darkness. It takes a few listens to understand that Mitchell didn't set out to replicate something like Sinatra's 1955 In the Wee Small Hours of the Morning long-player but instead made her own. Not emptily elegant or insipidly lush, Mitchell's new disc is layered, intense, and addictively nocturnal.