Fans of Linda Ronstadt have swooned over her voice, a powerful instrument that can blast the dust off an Everly Brothers classic and breathe new life into jazz and mariachi standards.  Yet what comes through most strongly in a recent documentary about the singer is the way she used her vocal abilities to call attention to the work of others.

“I can always do a harmony part,” Ronstadt says in a recent interview.

The film, “Linda Ronstadt: The Sound of My Voice,” airs on CNN at 9 p.m. on New Year’s Day after a recent theater run, and tells the story via a time-capsule of clips, video moments and Ronstadt’s own words of how the singer captured public fascination with her carefully chosen covers of tunes by Roy Orbison, Clint Ballard Jr. and Warren Zevon, among others. But it also depicts her knack for helping those whose efforts she believes demand a wider profile. Emmylou Harris confesses that it was Ronstadt who helped her through a difficult time after the death of her musical partner, Gram Parsons. It was Ronstadt who led the members of the Eagles to find each other, putting Don Henley and Glenn Frey in her backing band. And it’s Ronstadt who lends her voice to such landmark songs as Neil Young’s “Heart of Gold” and Little Feat’s “All That You Dream.” She would go on to put a new spotlight on various musical genres that might otherwise have gone unheard by some of her fans.

She’s done so much of this work that it can get hard to keep track of it all. When asked about the many songs for which she has provided background vocals, Ronstadt takes pains to point out her contributions to Young’s 1977 album, “American Stars n’ Bars,” but appears momentarily stumped by this reporter’s mention of her work on The Nitty Gritty Dirt Band’s 1979 cover of Rodney Crowell’s “Voila! An American Dream.” The single went to number 13 on Billboard’s Hot 100 chart that year. “I’ll have to dig it up,” she says.

CNN helped unearth the documentary. Executives came up with the idea to try to tell Ronstadt’s story at a brainstorming session that took place approximately two years ago, recalls Amy Entelis, CNN’s executive vice president for talent and content development, in an interview. “We are always looking for people who are known, but maybe their story is less known,” she says, noting that Jeff Zucker, president of CNN and chairman of WarnerMedia News and Sports, initially suggested Ronstadt as a potential subject.

Getting her cooperation was not a fait accompli. “It’s not that easy to secure everyone’s interest and collaboration,” says Entelis. CNN assigned the effort to James Keach, who had worked with the network previously on a documentary about singer-songwriter Glen Campbell. Ronstadt had already been approached by two producers, Rob Epstein and Jeffrey Friedman. And while the pair had her interest, they lacked funding, Entelis says – and there had been no assignment of TV rights for the final product. “The timing really worked out for this to come together, which doesn’t often happen,” she says.

For her part, Ronstadt had cast a wary eye on the idea of a documentary of her life. “There were several offers out there, and I said ‘No,’” she recalls. But Epstein and Friedman had worked on a documentary on the life of Harvey Milk that she was familiar with from PBS, and she says she thought, “If I have to make this one, it’s not so bad. Maybe I have a chance to stop the other ones.” She reached an understanding with the producers, she says: the documentary would have to be limited to the events she described in her 2013 memoir, “Simple Dreams.” After all, she says, “if it was based on the book, I think it would be fine, because it would be mostly true.” Booklist had described her memoir as a sort of safe place: “There are no tales of parental cruelty or substance abuse (someone in the CNN film alludes to potential use by Ronstadt of diet pills).

“The Sound of My Voice” is CNN’s second documentary about a musician who continues to tread an interesting path. Ronstadt no longer sings in public, citing the effects of progressive supranuclear palsy, which was initially diagnosed Parkinson’s disease. The documentary tackles her coping with it head on. One of its final scenes shows Ronstadt in the present day singing with members of her family – a sight viewers may never witness again. There is also an emotional interview with Emmylou Harris, who breaks down on camera while discussing the topic.

“She is my sister,” says Ronstadt of Harris, with whom she sang on the critically acclaimed “Trio” albums as well as another collection, “Western Wall.” Singing together “is very, very intimate, and you become very close.”

In 2015, CNN aired the documentary “Glen Campbell…I’ll Be Me,” a detailed look at the country singer of the title as he toured while grappling with effects from Alzheimer’s disease.   It also provoked an emotional response from people who watched it. CNN hadn’t commissioned that effort,  but was able to secure TV rights – and, says Entelis, its executives were surprised by the result.  “The audience reaction to that film on CNN was enormous,” she says. “I think it told us that so many people are dealing with Alzheimer’s in their family and to sort of see that disease through the eyes of someone they’ve admired and are still connected to was, ultimately, a very, very moving story. It told us a lot of things about what our audience is interested in.”

Viewers will no doubt also want to examine dozens of clips of past Ronstadt performances, and interviews with Dolly Parton, Bonnie Raitt and Don Henley, among others – including guitarist Bobby Kimmel, who played guitar in the Stone Poneys, the band that gave rise to Ronstadt’s solo career.

They won’t be surprised by Ronstadt’s candor when it comes to politics. This was someone, after all ,who dated politician Jerry Brown, a one-time presidential candidate who become governor of California. The documentary features a clip of Ronstadt speaking bluntly about U.S. policies while appearing on a talk show.

She is still not shy. While attending a ceremony held in advance of her recent Kennedy Center Honor, Ronstadt rebuked U.S. Secretary of State Mike Pompeo after he quoted her Everly Brothers cover: “As I travel the world, I wonder: When will I be loved?” he said to her in remarks during the ceremony.  Her rejoinder: “I’d like to say to Mr. Pompeo, who wonders when he’ll be loved, it’s when he stops enabling Donald Trump.”

Ronstadt says she had no plans to get into a political discussion, but her decision may have been sparked by Sally Field, who was also honored by the Kennedy Center, and who told the assemblage at the small ceremony that she was mindful of living in an era “where the truth is under attack,” Ronstadt says. “It just came of my mouth,” Ronstadt says of her remarks. “I felt like I had to stick up for Sally Field.”

In any case, says Ronstadt,  “he set himself up for that” by quoting the song.  “Nobody would walk past that.”

CNN’s documentary may be one of the last documents of Ronstadt’s career. She released a live album from a 1980 concert in February of this year, but believes she doesn’t have much more in her archives. “I think they’ve scraped the bottom of the barrel, pretty much,” she says. “If I didn’t put it out, there are pretty good reasons for it.”

Ronstadt still has an ear out for sounds she thinks others should hear. “I really love Sia,” she says. ”Her singing style – she’s really an original.” As for songwriters, she thinks today’s crop has to work hard to surpass people like Leonard Cohen, Joni Mitchell or Bob Dylan. One thing that is made clear by both the singer and the film about her: You don’t need to use your voice to hone in on a good tune.