Emmylou Harris is fond of telling a story about the time in the ’60s when she wrote a six-page letter to folk icon Pete Seeger, asking him whether she could authentically sing his style of music if she didn’t come from a truly rustic, hardscrabble background. Seeger wrote back, telling her that she shouldn’t worry about suffering, life will happen and there’s nothing she can do about it. The earnestness and authenticity that a young Emmylou expressed in that letter says an awful lot about Harris as a singer, one of country music’s all-time greats.

Harris’ heartbreaking vibrato doesn’t soar. It cuts like a knife. She’s a tuning fork for emotion, whether she’s mourning her late friend and mentor Gram Parsons (“Boulder to Birmingham”), breathing her own special light into Townes Van Zandt’s “Pancho & Lefty,” or sweetly offering up romantic resignation on “Hanging Up My Heart,” off her new album with fellow country great Rodney Crowell, Old Yellow Moon.

That Harris has become a country icon is largely due to Parsons, who gave her not only the musical break she needed, but an education in traditional country music.

Dreaming of becoming the next Joan Baez, Harris dropped out of UNC-Greensboro in ’67 and moved to Greenwich Village, chasing a scene that had already left. She worked as a waitress and married fellow songwriter Tom Slocum in 1969, the same year she released her debut album, Gliding Bird. They had a little girl together, but the marriage went south, and Harris moved back to Maryland, where her parents could help care for her daughter. It’s there in 1971 that Chris Hillman (Flying Burrito Brothers, Byrds) saw her perform and recommended her to Parsons, who was looking for a female vocalist to collaborate on his 1973 solo debut, GP. They met, and it changed her life.

“Country music, even though I was exposed to it, I just thought that I couldn’t be bothered with it. I could not hear the subtlety in it, I couldn’t hear the poetry in it,” she told The New York Times last year. “He thought I could sing country music. I started as a harmony singer, that was his way to kind of sneakily turn me onto this extraordinary body of music, and in singing country music I really found the place that my voice was supposed to be … I can’t imagine that I would have gotten to the place I am artistically or even vocally, if it hadn’t been for Gram.”

Though an untrained vocalist, Harris jumped in where it felt right, and Parsons gave her confidence to find her own way. Later when Harris got into bluegrass, she’d have to learn the greater discipline of three-part harmonies. Since then, her duet work has become a mainstay of her career, partnering her with Johnny Cash, George Jones, Bob Dylan, Elvis Costello, Mark Knopfler, and Lyle Lovett.

Rodney Crowell was actually Harris’ first duet partner after Parsons’ death. She’d been looking for songs to cover for her 1975 debut Pieces of the Sky and happened upon Crowell’s “Bluebird Wine.” That album would be the first in a string of seven consecutive gold albums.

Crowell was brought along on her first solo tour as rhythm guitarist and Harris’ duet partner. They were backed by members of Elvis Presley’s band (guitarist James Burton, pianist Glen Hardin, bassist Emory Gordy) and together they were called Emmylou Harris’ Hot Band. “We were these hippie kids working with these really high-price musicians,” Harris told NPR last year.

Old Yellow Moon is Harris’ first collaboration since 2006’s All the Roadrunning with Dire Straits’ Mark Knopfler. The new LP with Crowell also follows one of Harris’ finest albums, Hard Bargain, featuring more of the singer’s own compositions (11 of 13) than any album in years. Hard Bargain was also Harris’ best-charting solo release since 1980’s Roses in the Snow, the sixth of those seven gold records that started her career.

Though her friendship with Crowell has endured and deepened, the two never got around to making a duet album until last year. Old Yellow Moon not only reunites Harris with Crowell, but Burton and some other Hot Band players make guest appearances. Even her ex and former producer Ahern returns to handle the knobs. Maybe it’s that familiarity that makes the record feel as cozy as an old pair of shoes.

There are plenty of terrific tracks on Old Yellow Moon, including the album-opening Hank DeVito tune “Hanging Up Your Heart,” a reprise of that first Crowell/Harris pairing “Bluebird Wine,” Kris Kristofferson’s dark blues-abilly rave-up “Chase the Feeling,” and Crowell’s mournful “Open Season on My Heart,” which recalls one of the Red Headed Stranger’s sad ballads.

Old Yellow Moon is largely acoustic, but the sound is crisp and surprisingly driving. Though the subjects are often sad or wistful (“Back When We Were Beautiful,” “Here We Are”), the songs themselves maintain a brisk pace without trying too hard. Harris and Crowell’s voices are intertwined throughout, evoking shared comfort in a sometimes cruel and lonely place.

“I love the sound of two voices together,” Harris told Rolling Stone last year. “Whether it’s two women or two men or a man and a woman. It just creates a third voice, and I love the conversational aspect of it.”