Baby boomer rock star docs, a cottage industry of late, are not created equal. Two recent ones transcend the norm — David Crosby: Remember My Name and the lovely Linda Ronstadt: The Sound of My Voice, all the more poignant since Parkinson’s has deprived her (and us) of her incomparable singing for a decade. Whereas Crosby’s doc unpacks his crustiness and sins, the Ronstadt film — directed by Ron Epstein and Jeffrey Friedman, and featuring notable talking heads (and Santa Barbarans Karla Bonoff and the late Kenny Edwards) — celebrates the singer’s seemingly angelic countenance and stunning powerhouse voice, of which we get ample, inspiring evidence in the film. Arizona-born and partly of Mexican heritage, Ronstadt headed to Los Angeles at 18, became a global pop sensation with scores of hits and platinum albums, but somehow maintained her essential sweetness and driving musical curiosity — making stunning ventures into Gilbert and Sullivan, the Great American Songbook, and Mariachi. It’s a portrait of an artist with a heart like a restlessly creative wheel.