"Country music at its Big Bang was two different musics," says Burns. "The music of Jimmy Rogers, which is Saturday night, and the music of the Carter Family, which is Sunday morning. That's been in tension in all of American music and in American life, I would suggest, all the way through."
"We say about country music, 'Oh, it's about pickup trucks and good ole boys and hound dogs and six packs of beer.' And that is a part, but a very small subgenre of country music," Burns tells CNN of stereotypical takes on the genre from those who haven't been listening closely and fail to understand why the country sound, in its many forms, has resonated and endured across generations.
"It's really dealing with universal themes -- two four letter words most of us are uncomfortable examining all the time: love and loss. And when you realize that, that country music is dealing with these fundamental human experiences, 'I'm So Lonesome I Could Cry' -- No one has ever not known what Hank Williams was talking about," says Burns.
Through a staggering array of interviews with some of country music's most significant artists and industry titans conducted over eight years in his signature patient, methodical style, Burns reveals both the telling biographical details of the music's creators and also how the country sound has evolved and grown over time, borrowing, inspiration, like his previous subject jazz, from a wide swath of musical influences.
"We tend to think of country music as one thing, but it's always been many things," says Burns. "It omnivorously wants to grab cowboy music and western swing, and the Bakersfield sound and the Nashville sound, countrypolitan and all the various permutations of string bands up and down Appalachia, one of which branches off into a whole new genre called bluegrass. It's never ending and it's omnivorous and it's not a separate silo. It's always been connected. There's no border. No passports required, that allows you to go into R&B or allows you to go into jazz or allows you to go into folk or rock. It is, in fact, one of the parents of rock with R&B."
In Burns' view, the genre has also minted some of the finest songwriters in popular music, country or otherwise.
"There are no greater poets of music than Hank Williams or Kris Kristofferson or Johnny Cash or Loretta Lynn or Dolly Parton," he says. "And they sit there with Lennon and McCartney and some of the American Songbook folk and blues men and folk people like Dylan. And they coexist and they all recognize each other. Everybody is connected."
Burns said the musical interconnectivity would become a pervasive theme within the documentary, putting the lie to the notion that there are any rules to what is and is not "pure country."
"We're in an age when everybody wants to suggest that we should separate and go back to some pure, singular American thing," he says. "It never existed. We've always been a mutt. We've always been a mongrel. And if you try to say that country music is identified more with that, you're already in trouble because it's just not true."
But amid the ever-present desire to borrow and blend other musical forms, there's also a strong sense of tradition. Burns discovered many enduring, sometimes contrary truisms among the country music community, which displays a more prominent sense of family than other musical genres.
"You may not have had a hit, someone says in the film, for 30 years, but you're still part of the family," he says of the prevailing ethos.
"There's also the fact that it is literally families," Burns adds, noting that country greatly values its linage and legacies, celebrating multigenerational clans, like Hank Williams, his children Hank Williams, Jr., and Jett Williams, and grandchildren Hank Williams III and Holly Williams; and the Carter Family Singers, Johnny Cash and June Carter and their children Roseanne Cash and John Carter Cash. "But it's also the family of the musicians, of playing on the Opry stage and then getting in a bus or a car and touring for a week and madly getting back in time to appear underpaid on the Grand Ole Opry stage and then back to the more lucrative event."
That sense of family and familiarity creates a bridge between fans of country music and the stars at its center, as well as a lived-in authenticity to the often tortured, often rowdy personal experiences expressed through the music.
"Other music genres are separated and isolated by celebrity, by bold faced names," says Burns. "They're going through that same stuff, and People Magazine's going to discover them and ferret it out and tell you, or the tabloids will. But with country it's right in your face. You know what's going on when somebody miscarries. You know when this person's marriage is over or when somebody falls in love. That's a particularly intimate thing."
Certain country stars can mine that intimacy and goodwill for decades, as long as their talent prevails -- Dolly Parton being a case in point.
"I'd put her on the Mount Rushmore right away," says Burns. "Her voice is one of the greatest gifts from God any singer has ever been bestowed with. She is a phenomenal song writer ... She's this great businesswoman and she's funny and she's self-effacing. She's a good human being. She makes fun of herself. So she's the total package, as somebody says in the film."
Burns points to Paton's song "I Will Always Love You," which in the documentary she shares the song was written in an emotional bid to separate from her longtime mentor Porter Wagoner -- an effort that ultimately won Wagoner over and allowed her to pursue her solo ambitions (though he insisted on producing the inevitable hit as a reward).
"When you find out why she wrote it, it elevates her version of it to equal with Whitney Houston, where you never thought anybody could beat Whitney. When you know the story behind the story, all of a sudden she achieves a kind of parity with it,' Burns says.
Another of the many country legends who appears on camera is Willie Nelson, who despite penning hits established stars, like Patsy Cline's "Crazy," initially struggled to break through as a singer-songwriter in his own right.
"His phrasing owes more to jazz than it does to any country rhythms, and that's what made it hard for him to fit it into Nashville," says Burns. "They couldn't figure out what to do with his phrasing and he needed to retreat to his native Texas, where they loved him and took him for what he was."
When Nelson finally agreed to sit down for an interview, Burns worried he might retreat into his habit for notoriously taciturn responses, but was pleasantly surprised.
"By the time we got to his story, he really opened up and was incredibly moving," he recalls. "At one point, disappointed in his life's trajectory and his career, he got drunk at Tootsie's and went out in the middle of Broadway and laid down, as he said, in the middle of the highway, and didn't wake up dead. He woke up a got up and said, 'I'm still here,' and eventually left and, as you know, made a name for himself."
The filmmaker says that, through what becomes very apparent through the conversations with scores of artists and icons from the genre's earliest and ending in the pop-crossover boom years of the 1990s, is that country music creates a unique, emotional bond between performer and audience -- more personal connection than idol worship.
"One person in the film says, 'You don't go up to Frank Sinatra and say "Hey, Frank -- great set!"' laughs Burns. "But you do go up and you look Kathy Mattea in the eye and you don't say anything and you start to cry and she hugs you and you hug her, and then as you're moving away, the husband trails behind and says 'She buried her mom this morning, but she really wanted to be here.' That's country music."