There's a moment in Linda Ronstadt: The Sound of My Voice -- a documentary about the legendary artist -- that arguably sums up the apex of her singing, versatility and popularity.

It didn’t happen during Ronstadt’s pop-star phase in the '70s, but rather when she appeared in the Broadway (and later film version) of Gilbert and Sullivan's operetta The Pirates of Penzance in the early '80s. For someone regarded as more of a rocker, Ronstadt made the role of Mabel truly her own, reaching high notes normally reserved for a professionally trained opera singer. Fans and critics who saw her perform in that production probably wondered at the time, “Is there anything she can't do?”

The Pirates of Penzance is just one example of the many triumphs from throughout Ronstadt's storied career, as documented in the movie by directors Rob Epstein and Jeffrey Friedman. While The Sound of My Voice doesn't offer any revelations that haven’t already been uncovered (most major stories were laid out by Ronstadt herself in her 2013 memoir Simple Dreams), the documentary is a touching tribute to the singer, especially in the context of the Parkinson's diagnosis that forced her to stop singing in 2009.

The film's narrative is driven by both Ronstadt (who mainly appears via archival footage) and a bevy of famous collaborators and friends. Emmylou Harris, Dolly Parton, Jackson Browne, Don Henley, Aaron Neville, J.D. Souther, Bonnie Raitt and longtime producer Peter Asher are among those interviewed.

The Sound of My Voice begins with the singer's upbringing in Arizona. Raised in a musical household, Ronstadt's gift was evident from an early age. Her first taste of fame occurred in 1967 when, as a member of the Los Angeles-based group Stone Poneys, she scored a Top 40 hit with the Mike Nesmith-penned “Different Drum.”

After the band’s breakup, Ronstadt recorded a number of solo albums for Capitol Records that achieved varying degrees of success. Her career took off with the 1974 LP Heart Like a Wheel, launching a fruitful collaboration with Asher that resulted in a string of hit albums (Simple Dreams, Prisoner in Disguise, Living in the USA, Mad Love) and singles (“You’re No Good,” “When Will I Be Loved,” “Blue Bayou,” “Hurt So Bad”). The film not only documents the peak of Ronstadt’s popularity as the preeminent female pop singer of the ‘70s, but also the emotional toll that celebrity and whirlwind success took on her.

Feeling stifled by the pressures of fame, Ronstadt stylistically branched out in the early ‘80s, beginning with her performance in The Pirates of Penzance. She further upped the creative ante with her interpretations of popular standards in collaboration with famed arranger Nelson Riddle, and then later recorded Mexican mariachi music on her 1987 album Canciones de Mi Padre. These musical left turns didn’t slow her viability as a hit-maker, as evident on the hugely successful 1987 LP Trio, record with Parton and Harris, as well as her duet with Neville on “Don't Know Much” in 1989.

The story concludes with Ronstadt's retirement after being diagnosed with Parkinson's disease and her coming to grips with never singing to audiences again. There's a moment near the end featuring the singer in the present day that will both surprise viewers and may even bring a tear; it is an example of resilience and determination.

The Sound of My Voice isn't just about Ronstadt's life and music, but also the history of Southern California rock music during the '70s; in a way, she's the thread connecting many of the artists interviewed in the movie. For example, the members of her early backing band later became the Eagles. At a time when men dominated the music industry, Ronstadt befriended and provided support to female artists such as Harris and Raitt. In addition to interpreting popular songs, she performed original tunes by then-unknown songwriters like Karla Bonoff, Kate and Anna McGarrigle and Warren Zevon. All of these examples further display Ronstadt's far-reaching influence throughout the music world.

The singer, who’s known for her perfectionism in the studio and onstage, also took several artistic risks, most notably the Spanish-language album, that challenged conventional record company wisdom. And Ronstadt’s dedication to honoring her Mexican heritage through music seems all the more timely given the current political climate.

Unlike most other rock docs, there is nothing salacious or gossip-driven in The Sound of My Voice. Aside from her childhood, the only other personal aspect of Ronstadt’s life touched briefly in the film is her former romantic relationship with then-California governor Jerry Brown. Instead, the filmmakers focus on delivering the fascinating life story of an influential artist and her unmatched career. Well-executed and poignant, The Sound of My Voice honors a pioneering musician whose passion for singing took her to stratospheric heights.

Linda Ronstadt: The Sound of My Voice opens in theaters on Sept. 6.

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