There's that thing about Sturgill Simpson's voice you could call nostalgic -- that deep country twang, an inflection impossible to fake, first invented by Merle Haggard or maybe someone else, carried forth by Waylon Jennings, George Strait, Alan Jackson, and Toby Keith. The instant joy at that hearing it, so simultaneously full of soul and restraint, on a new record as sharp as Simpson's Metamodern Sounds in Country Music is largely rooted in nostalgia for that good old fashioned outlaw country and all its attendant truck stops and blue jeans and hickory wind.

But it's obvious -- and it was even more obvious last night (Feb. 13), at Simpson's sold-out show at Music Hall of Williamsburg in Brooklyn -- that Simpson has so much more up his sleeve, more, even, than lyrics about tripping on hallucinogenics and being visited by reptile aliens. If nowhere else but musically, Simpson takes boot-stomping country to realms heretofore uncharted, at least by the likes of Waylon and company.

Simpson's guitarist, Laur Joamets, is almost unspeakably good, tastefully melodic and technically dazzling. The rest of the quartet, Simpson included, chases down -- dare I say it? -- Phish-like grooves that roar for several minutes, like the funky freakout embarked upon on "Some Days," from Simpson's 2013 debut High Top Mountain. Plenty of Old Time Country Revue-style acts put on the twang and can burn through a fast hillbilly stomp to the delight of anyone with ears, but Simpson seems to be onto something a little freakier.

The same goes for "Old King Coal," a song about the post-industrial blight of Simpson's home. Before kicking into the song, Simpson pointed to someone in the crowd -- "that girl in the front row graduated the same year" from the same high school, he said -- then sang about the curse of living in a ruined place, where "the rivers run muddy and the mountains are bare." Similarly, "Just Let Go" is, hands down, the most moving country ballad I have ever heard about surrendering your soul to the Bardo.

Add to those lyrical adventures, both anthropological and metaphysical, a sense of country music authority derived both from that natural inflection and his Kentucky coal miner lineage. Therein lies Simpson's singular appeal; it's not just the reptile aliens -- Simpson is the only country singer with this kind of authority who takes this many risks with song structure and subject matter, and for those with a mind for traditional country and more adventurous music, it's a sublime experience. Analyzing the audience at a venue like Music Hall of Williamsburg isn't particularly fruitful -- same dude-heavy, Patagonia-wearing group as every other show I've seen there -- but it was a crowd that enthusiastically and physically showed their appreciation for both the boot stompers and the acid excursions.

There was also a considerable amount of enthusiasm for opener Anderson East, who has a voice out of all proportion to his humanity, like a supercharged monster truck engine packed inside a Jeep. His voice is like Bob Seger's but last night it escalated to vocal cord shredding levels. The set smacked a bit of what they call "blue-eyed soul," stripped somewhat of its invention, a bit neutered but overemotional, recalling Johnny Lang and Ray LaMontagne. It's not as exciting as the wandering country that Simpson plays, but the audience's ecstatic reaction to it says something about the crowds that come out to see him play.

Simpson's 22-song set ended with a raucous version of the Osborne Brothers' 'Listening to the Rain,' spliced with T. Rex's 'The Motivator.' Simpson's music may have that country music grit that would do Waylon Jennings proud, but what makes it exciting is how Simpson uses that authority -- along with wit and boldness -- to push the music forward on his own whim.

Sturgill Simpson — Setlist, Feb. 12, 2015
"Sitting Here Without You"
"Water in a Well"
"Long White Line"
"Poor Rambler"
"Time After All"
"Medicine Springs" (Stanley Brothers cover)
"A Little Light"
"Living the Dream"
"Life of Sin"
"The Storm"
"Sometimes Wine" (Sunday Drivers cover)
"Old King Coal"
"Some Days"
"It Ain't All Flowers"
"The Promise" (When in Rome cover)
"Railroad of Sin"
"Just Let Go"
"You Can Have the Crown"
"Turtles All the Way Down"

"I'd Have to Be Crazy"
"Listening to the Rain" / "The Motivator" (Osborne Brothers cover/T. Rex cover)