Marcus Mumford’s voice gave his band’s songs some much-needed gravity. (All photos by Kyle Gustafson/FTWP)

Marcus Mumford is the 24-year-old singer of Mumford & Sons, the West London folk-rock quartet whose 2009 debut album “Sigh No More” has reportedly sold more than three million copies worldwide. Performing for a capacity crowd at Merriweather Post Pavilion on Thursday night, Mumford’s over-the-top bandmates — who he’s not actually related to — were irritating in a number of ways.

Multi-instrumentalists Ben Lovett, Ted Dwane and “Country” Winston Marshall each contributed plenty of hooting, hollering, moon-howling and other facial contortions to an array of very-earnest folk-rock songs that pined for a more subtle touch. But subtlety is not their thing. At times, Marshall would pluck at his banjo while thrusting his pelvis like a bluegrass Rick James. Freak folk, indeed.

These sweaty displays of cathartic enthusiasm all felt like big, dumb distractions from the band’s sonic centerpiece, Mumford’s voice. With plaintive vowels buzzing handsomely out of his mouth, he played both the frontman and the straightman, giving the set’s most hard-charging fare a much needed center of gravity.

“It’s empty in the valley of your heart,” Mumford sang, poised as his bandmates tiptoed around him. “The sun, it rises slowly as you walk/Away from all the fears and all the faults you’ve left behind.”

But those words were made only more bittersweet by the fact that you knew exactly what came next: a lone kick drum thump-thump-thumping like a bleeding heart, only to announce another jugular-popping crescendo, all four band members yelping in harmony. With practically every selection in the Mumford & Sons songbook following this pattern, things got exhausting. Then, annoying.

Rapt fans may have begged to differ. The fascination with Mumford & Sons, and similar groups on the rise, appears to stem from technology fatigue. After spending our daily lives sleepwalking through intangible digital bandwidth, we want to see artists that play actual instruments: banjos, accordions, fiddles, a big ol’ upright bass. The old-timier, the better. The sweatier, the better. Both imply authenticity. This music is “real.”

But it also needs to be “good,” and all the instrument-swapping onstage proved that none of these guys are truly dynamite players — although Mumford’s hamfisted time-keeping behind the drum kit during “Lover of the Light” had its charms.

There wasn’t a lot of air-drumming, but the swollen crowd continually emptied their lungs, presumably singing themselves hoarse to Mumford’s every syllable.

Chill-pills for his bandmates, lozenges for his fans.