"I know what Americana is," Scott Avett told the packed-in, elbow-to-elbow crowd gathered at Nashville's Riverfront Park Saturday night (Sept. 20) for this year's Americana Music Festival.

"Americana is something that allows us to be what we want to be, allows us to be what we need to be and allows us to be what we are," he said.

With countless definitions applied to the seemingly boundless genre, the thunderous applause his sentiment received seemed to indicate that this one just might be the best one offered so far.

The truth of this interpretation is certainly embodied in the sound and the spirit of the Avett Brothers, one of Americana's most dynamic and diverse acts. As they transported the audience through a two-hour-plus set of lively originals and tasteful covers, they drew from classic country, traditional folk, bluegrass, rock, punk, ragtime and doo-wop. While no two songs sounded the same, they all still managed to sound like the Avett Brothers.

The show's cinematic opening involved a drum-led quartet of stringed instruments, filing out one by one, playing the melodic introductory lines of "Satan Pulls the Strings." By the time brothers Scott and Seth joined the fray and added their banjo and acoustic guitar to the gypsy folk bounce, the audience was in a full-blown free-for-all. Even though this song only debuted earlier this summer and has yet to appear on any of their albums, the audience responded as if it had been in their catalog for years.

The note-for-note sing-alongs to practically every song proved there was no discerning between longtime fans and brand new converts. The band played older songs going as far back as 2003's A Carolina Jubilee for "The Traveling Song" and the kazoo-led "The D Bag Rag," while last fall's Magpie and the Dandelion was represented with "Morning Song" and "Vanity." However, for the bulk of their set list, the Avett Brothers pulled heavily from their Emotionalism and I and Love and You albums with each uproarious response signaling audience approval of this decision.

With so much audience engagement, the quieter acoustic songs like "Laundry Room" and "Murder in the City" turned into campfire choruses, while the rapid-fire hopscotch lyrics of "Distraction #74," "Talk on Indolence" and "Slight Figure of Speech" tripped up only a socially-lubricated select few. In fact, the only time the audience showed a revered restraint was when Scott and Seth joined bassist Bob Crawford for a one-guitar, three-part-harmony take on the hymn "In the Garden," introduced with a touching word from the brothers: "Here's an old gospel song we learned from our father."

Appealing to both the Americana atmosphere and the Nashville locale, the Avett Brothers even threw in a few choice covers, including George Jones' "The Race Is On" and the traditional folk covers "Old Joe Clark" and "Little Sadie." They closed the show with a straight-on doo-wop standard, "Goodnite, Sweetheart, Goodnite," with the familiar refrain being sung by the attendees long after the Avett Brothers had left the stage.

Earlier in the night, the Lone Bellow opened their portion of the show with "You Can Be All Kinds of Emotional," a song that perfectly describes the vocal aura of lead singer Zach Williams. Whether he was softly crooning through the tender ballad "Tree to Grow" or hollering like an old-time preacher in "Bleeding Out," Williams held both his voice and the Riverfront audience in his complete control for the entirety of their 11-song set.

As shamanesque as Williams can be though, the truly unique sonic secret of the Lone Bellow lies in the way his voice and energy unite with mandolinist/vocalist Kanene Pipkin and guitarist/vocalist Brian Elmquist. No matter how boisterous one of their songs can get -- the percussive gallop of "Green Eyes and a Heart of Gold" comes to mind -- the powerful sound created when the trio sings together unquestionably outshines everything else going on. This was never more evident than when the three joined around one microphone with just an acoustic guitar to harmonize on the gospel-tinged number "Watch Over Us."

Pipkin and Elmquist were equally vivid in their individual contributions as well. Pipkin drew a flood of approving cheers during her first solo verse in "You Don't Love Me Like You Used To" and Elmquist -- sporting the best untamed hair-flop this side of Jerry Lee Lewis -- transformed the crowd into a congregation during his speedy Sunday morning stomper, "If Heaven Don't Call Me Home." With a couple of unreleased songs like this showing up on the set list, it was no surprise when Williams mentioned they were in the process of making a new record.

Prior to the Lone Bellow's set, Texas troubadour Shakey Graves got the Riverfront crowd clapping, stomping, and singing along with his countrified garage rock concoction that features elements of Delta blues, country folk and psychobilly energy. Backed only by his buddy Boo on drums, the kinetic duo debuted songs from their next album, And the War Came (out Oct. 7), as well as a few old favorites thrown in for good measure.

While the rowdy railroad shuffle of new songs "Hard Wired" and "Big Time Nashville Star" got the crowd up and dancing, it was the two older songs Graves played by himself that garnered the most connective moments. With his right foot pounding out a beat on a makeshift kick drum and his left foot playing a tambourine, Graves rattled off his road song "Built to Roam" and the dirty waltz of "Word of Mouth" to rambunctious applause.

Kicking off the evening's festivities was Angaleena Presley, affectionately known as "Holler Annie" to fans of her platinum-selling country music trio Pistol Annies (along with Ashley Monroe and Miranda Lambert). Presley was finishing out a busy Americana Fest week that also included appearances at Tuesday night's kickoff bash at the Basement, Wednesday night's Americana Music Awards show (where she and Kacey Musgraves presented Loretta Lynn with a Lifetime Achievement Award) and Thursday night's official showcase at the High Watt.

In only her second show fronting her four-piece band, Presley seemed right at home treating the attentive crowd to songs from her upcoming debut solo album, American Middle Class (out Oct. 14). One charming moment of fan interaction occurred just as Presley was finishing up "Better Off Red," her wistful ode to her hometown of Beauty, Kentucky. After one enthusiastic fan's homespun howl, Presley called out, "Who yelled, 'Yee-haw'? You're my favorite."

From the Southern thump of the title track, "Pain Pills" and "Knocked Up" to the slow burn blues of "Ain't No Man" and "Grocery Store," Presley smiled, smirked and snarled her way into the musical hearts of those who were already her fans and those she was adding to the list with each new song she played.