What made Motown great? What is it about Stax recordings that gives them that distinct sound? Why do so many country hits come out of Nashville? Why is Exile on Main St. considered one of the greatest Rolling Stones albums?

A number of hypotheses could apply to any of these questions, but only one answer applies to all of them: They all feature great session musicians.

The Funk Brothers, Booker T. & the M.G.’s, the Nashville A-Team, Billy Preston. Session players are an unheralded bunch who often provide the sound, feel, and color to the music we love. So what does it sound like when session musicians step into the spotlight?

Chris Wagoner and Mary Gaines are masters of their craft — veteran session players who can wail on anything from lap steel to ukulele. Primarily though, Wagoner plays the violin and Gaines plays cello. For more than three decades, they’ve been the rug that holds the room together for an impressive canon of local, national and international artists. Their recording credits include everything from Madison’s own Harmonious Wail to singer-songwriter Carrie Newcomer to Smashing Pumpkins’ 1991 genre-defining album Gish.

Local aficionados may have seen the wife-and-husband duo perform in one of their several jazz-grass inflected incarnations over the years — the Stellanovas, the Common Faces, the Moon Gypsies or Graminy. Finally, Gaines and Wagoner have released their first EP as … Gaines and Wagoner.

LO-Fi EP No. 1 is a six-track tour through Gaines and Wagoner’s diverse songbook, touching on bluegrass, jazz, Americana and blues in under 30 minutes. Recorded and mixed by Wendy Schneider at her recently reopened Coney Island Studios on the east side, the result is a rich production that shows off the duo’s finely tuned arrangements, harmonies and depth of sound.

The album begins with two smooth originals, “Lazy” and “Halloween,” which showcase the duo’s songwriting ability, reminiscent of John Prine’s devilish commentary wrapped in Midwestern folksiness.

The EP builds to a rockabilly finish with a gritty, stomping version of Mose Allison’s “Parchman Farm.” The highlight of LO-Fi No. 1 might be the preceding track, a take on John Hartford’s “Steam Powered Aero Plane.” It’s here where Wagoner hits peak fuzz-wah fiddle in a funky version that sounds something like Bill Monroe if dosed by Jamiroquai. Punchy rhythms from Gaines’ plucked cello and Erik Radloff’s percussion come through crisply throughout.

By all accounts, a live show involving Gaines and Wagoner is a high-wire act of improv chemistry that you’ll only find with people who have been playing (and living) together for decades. That’s what makes this disc a notable release; the duo carefully crafted this EP, and it proves to be a demonstration of their prowess in producing their sound in a studio.

Followers of Madison’s substantial local jazz scene will want to add this album to their collections. They’ll have a chance to hear the duo live at the CD release party June 8 at the Brink Lounge at 9 p.m. More good news: There’s talk of a crowdfunding campaign to send them back into the studio.