Sturgill Simpson won many fans with his 2013 debut album, High Top Mountain.

It is unapologetic in its evocation of '70s outlaw country.

For his sophomore date, he and his band entered a Nashville studio with producer/engineer Dave Cobb (Jason Isbell), and cut Metamodern Sounds in Country Music live-to-tape in four days.

These songs and their production values, though immediately reconizable, are more varied and textured than those of his debut--there's no pedal steel here for one thing.

The Waylon Jennings-esque quality in Simpson's singing voice remains, but that's built in.

His songwriting and confidence have grown exponentially.

The set is introduced by his 82-year-old coal-mining grandfather Dood Fraley on opener and first single "Turtles All the Way Down." The track features Cobb's nylon-string guitar, the wafting tapes of a Mellotron, electric bass, acoustic and electric guitars, and sharp drums framing Simpson's lyrics that refer to Jesus, the Old Testament, Buddha, mythology, cosmology, drugs, and physics, before concluding that "love is the only thing that saved my life," making it a glorious cosmic cowboy song.

On the rocking "Life of Sin," Simpson's acoustic guitar meets Laur Joamets' razor-sharp Telecaster leads in a cut-time shuffle that explodes in a country boogie.

"Voices" addresses the collective and troubled history about coal-mining with wisdom--all inside a spacious yet lean three-minute country song.

There are two covers here: One is a killer reading of Charlie Moore's and Bill Napier's trucker anthem "Long White Line" that careens and chugs with Joamets' razor-wire Telecaster and Simpson's flatpicking.

The other is "The Promise." Originally a hit for the British pop band When in Rome in 1989, Simpson utterly transforms it into a progressive honky tonk love song and makes it his own.

"A Little Light" is rockabilly-country-gospel with wrangling guitars, handclaps, ragged-but-right vocal harmonies, and plenty of spiritual swagger.

"Just Let Go" is Buddhist gospel, with gorgeous harmonies, spiralling mellotron, slide guitars, poetic lyrics, and organ--it's one of the set's finest moments.

It introduces the acid-drenched psychedelic country that is "It Ain't All Flowers." Simpson's prescient, philosophical lyrics are framed inside phased, wah-wah'ed, and reverbed guitars, crunchy snares, haunting mellotron, spacy slide lines, and instrumental backmasking that wind into the stratosphere.

His strident, passionate vocal is so tough, soulful and spiny, it bleeds through genre definitions as it rocks, rolls, and wails.

Metamodern Sounds in Country Music is wildly adventurous; it extends the musical promise outlaw music made to listeners over 40 years ago.

Simpson is too honest, restless and dedicated to country music's illustrious legacy to simply frame it as a musical museum piece.

As an artist of uncommon ability, he has learned from its hallowed lineage and storied past that in order for it to evolve, it cannot be reined in; it must be free to roam in order to create its future.

His visionary work on this album opens the gate wide on that frontier.