Acappella music has enjoyed a surge in popularity over the past decade, as evidenced by the success of Pentatonix and the “Pitch Perfect” movies. Few things compare to the emotional power of the human voice, but it is surprising that a cappella found mainstream favor when pop audiences routinely expect elaborate production values.

“In many ways it is countercultural to much of the popular music we hear,” concedes Jeff Smith, artistic director of m-pact, who’ll give a rare local concert at Caltech Saturday. “A cappella music by its very nature is raw.

“There are certainly ways to enhance the production value to a certain degree, but at the end of the day, what you have are vocalists producing music right there onstage, live, with nothing between themselves and the audience but a microphone. I think that provides a unique connection, especially when you add the element of improvisation that we like to include.”

The group was initially formed as a quintet in Seattle in 1995, with the idea of fusing the harmonic sophistication of vocal jazz ensembles like Take Six and Manhattan Transfer with funk and rock sensibilities and a vocal rhythm section. Oklahoman Smith, who joined after m-pact relocated to Los Angeles in 2004, expanded ranks to a sextet. The self-described “elder statesman” oversaw an energizing “reboot” when the two remaining original members retired in 2016, and now anchors a lineup featuring San Jose’s Drew Tablak, Texan Aaron Schumacher, Connecticut’s Andy Degan, Long Beach’s Jamond McCoy and New Yorker Tracy Robertson.

But why all male voices? To achieve particular vocal textures?

“You know, that’s a good question,” Smith says, conjecturing that m-pact founders primarily knew other male singers. Now, however, the ensemble’s “wow factor” derives from their wide range: “from very high ‘male soprano’ voices to very low bass voices and everything in between — with an all-male ensemble. You would lose some of that wow factor if there were females involved.” That said, he hastens to add, they have occasionally hired female singers to sub when the male singers capable of hitting those top notes could not be found.

They don’t consider their material “covers” because their arrangements differ so dramatically from the originals. A number of m-pact recordings have been released since 1996, and current members are writing an album for release early next year. They’re also developing a Motown-themed show to be performed with symphonies. Saturday’s a cappella concert will be comprised of jazz standards and songs by the Beatles, Earth Wind & Fire, Jackie Wilson, Stevie Wonder, offbeat contemporary artists like Jon Bellion, Emily King and Vulfpeck. Clever beatboxing and harmony arrangements freshen pop and soul classics like “Come Together” and “Don’t You Worry ’Bout a Thing,” which still feel positive and timely.

“We try not to mess with melodies,” Smith says. “You can re-harmonize in a way that tells the story slightly differently, and change the tempo, groove and mood of a song without changing melody at all. Melody and lyrics are the essence of the song.”

m-pact at Caltech’s Beckman Auditorium, 1200 E. California Blvd., Pasadena, at 8 p.m. Saturday, April 21; $32-$42, $10 youth. Info/tickets: (626) 395-4652.,