For Fall Out Boy frontman Patrick Stump, serving as a judge on NBC’s “The Sing-Off” two-hour special at 7 p.m. Wednesday (WMAQ-Channel 5) is a whole new twist in the Evanston native’s music career. Calling the other day from Los Angeles, Stump called the “crazy-good opportunity” an intriguing new chapter for him.

“It’s interesting because while I’m a producer and so have kind of acted in a similar capacity on records and things like that, this is the first time I’m really dealing with a cappella music.

“The strength I bring to the table is that I’m looking at this judging as looking at any kind of music. I have an interest and appreciation for a cappella music, but while it’s not my special aptitude, I think I’m a pretty good judge of what’s good and what’s not.”

Stump particularly loves the fact that “The Sing-Off” is all about pure singing, with no instrumental support to hide behind.

“I think that’s true, especially in a group setting like we have here,” said Stump, speaking about the six finalists who will compete for the $50,000 top prize Wednesday: Nashville-based Timothy’s Gift and the Melodores; the Exchange from Los Angeles; Traces out of New York; Northern California’s San Fran 6, and A. Squared, who hail from New Haven, Connecticut.

Patrick Stump (left) judges "The Sing Off" with  Jewel and Boyz II Men's Shawn Stockman. | NBC

Patrick Stump (left) judges “The Sing Off” with Jewel and Boyz II Men’s Shawn Stockman. | NBC

“Nothing to hide behind — that’s the key,” added Stump. “You have to be every kind of instrumentalist at once when you’re doing the a cappella thing. One of the things I really love about ‘The Sing-Off’ is that they’ve focused on a kind of forward-thinking approach to a cappella. It’s not the standard a cappella singing we’re used to — like with barbershop [quartets].”

Stump hastened to clarify that he is also a fan of well-done barbershop singing, “but the show has redefined what can be done with a cappella singing. Now, because of that, you have to be the drummer. You have to be the bass player. You have to be the keyboards. You have to be everything. Everyone one has to be a beat-boxer and Mariah Carey — all at once!”

Talking about other musical competition shows like “American Idol,” “The X Factor” and “The Voice,” Stump said they made success possible for groups and singers who might never have made it without that exposure. He pointed to Pentatonix, the hugely popular group (who also will perform on Wednesday’s show) that won season three of “The Sing-Off.” “They’re magic — there’s only one of them. It just shows you how limitless this experience can be,” he said.

“I’m a rock musician. You hear within the rock community this distrust of competition shows. I’m like, ‘Yeah, but it totally leveled the playing field.’ You have groups like Pentatonix who never before would have existed in the pop landscape. Now they have a massive Christmas record and they are legitimate players in pop music now because of their ability showcased to a national audience on ‘The Sing-Off.’ ”

Before he hung up, Stump brought me up to date on Fall Out Boy — performing Thursday at the Allstate Arena in 103.5 KISS FM’s Jingle Ball — and his own solo career.

“Right now, I’m in the thick of Fall Out Boy,” he said, noting a new album comes out Jan. 20. “We just finished it. It’s called ‘American Beauty, American Psycho.’ ”

As for his non-Fall Out Boy plans for 2015, Stump said, “I’m looking to do some more producing stuff this coming year. I can’t wait. It’s going to be a good year, I can feel it.”