A cappella groups saw their heyday when “Glee” became a big hit on Fox 14 years ago and led to the reality competition show “The Sing Off.”

On the third season of that show, a quintet called Pentatonix was named the victor and embarked on a career that has made them by far the biggest a cappella act in the world. Over 12 years, the group has toured Europe, Asia and North America multiple times, pocketed three Grammys and released 11 studio albums, including a myriad of Christmas-themed albums, videos and TV specials.

They are now on the North American leg of their current tour.

Since winning “The Sing Off,” they have kept four original members but brought in one replacement when bass singer Avi Kaplan decided to embark on a solo career in 2017. They quietly auditioned a new person, who ended up being Matt Sallee.

“I’m still pinching myself,” Sallee said in a recent interview with The Atlanta Journal-Constitution. “We got a Hollywood Walk of Fame star earlier this year, and just being there and seeing how inspiring they are to so many fans was incredible.”

Sallee was certainly well qualified. He was a long-time a cappella man prior to joining Pentatonix.

Sallee, a Baltimore native, grew up with a music pastor father and musical theater in his heart. He graduated from the Berklee College of Music in Boston and worked in wedding bands. Ben Bram, Pentatonix producer, knew of him. After Kaplan left, Bram asked Sallee to audition for a bass part in a major a cappella group that was going to tour overseas.

Bram didn’t tell him upfront who he was auditioning for, but Sallee figured it out given that only a handful of a cappella groups could do a tour like that. At callbacks in Los Angeles, he nervously sang John Lennon’s “Imagine” with the four other members for the first time.

“It’s a really hard arrangement,” Sallee said. “It goes high and low and there are a lot of sustained notes. The bass is the foundation. It looks easy, but it’s difficult. We then stood in a circle and did ‘Daft Punk.’ That’s when I knew I had a chance.”

He waited for months for an answer, thinking at one point he didn’t get the job. Then he got the call, which surprised him. On the road, he even got to meet departing member Kaplan, who gave him his blessing. “It felt like a true passing of the torch,” he said.

Sallee wasn’t sure if the fans would accept him, but when a fan found a picture of him online meeting the band five years earlier, they figured he was one of them. “The Pentatonix fan base is a beautiful community,” he said.

His first live gig with Pentatonix in 2017 was a concert for an opening of a Sak’s Fifth Avenue in Toronto. On the bus, the others decided to change a few songs out at the last second. Fortunately, he said, he was prepared: “I had done my homework. I knew every Pentatonix song. It went off fine. I was able to trust my training.”

This current concert tour features the group’s usual crowd-pleasing mix of originals, covers and medleys, along with a new original song called “I Rise.”

“It’s an anthemic song about soldiers fighting and overcoming adversity,” Sallee said. He wrote it with two other Pentatonix members and veteran songwriter Lauren Christy, known for Avril Lavigne’s breakout hits “Complicated” and “Sk8ter Boi.” He said the reaction from the crowd was solid on night one.

The concert is not devoid of instruments. Sallee at one point even plays the drums. “It was nerve-racking,” he said.

As for the over-arching appeal of Pentatonix, he said the magic was there the minute he saw them on “The Sing Off” 12 years ago.

“It was the first group to me that was able to cover popular songs well,” he said. “They could do ‘E.T.’ by Katy Perry and ‘Your Love is My Drug” by Kesha and ‘Love Lockdown’ by Kanye. Such versatility! You can hear the individual voices so well. It was seamless. And being part of Pentatonix now, it’s extremely special and unique.”