When the Summerfest headliners were originally announced, wildly popular a cappella group Pentatonix was one of the most intriguing names headed to the Big Gig. I knew I wanted to see the show, partly because, back in college, I was in a cappella group and partly because I saw the band back at its first show in Milwaukee at The Pabst Theater – and even further back when they won NBC’s "The Sing Off" – and was rather impressed.

The main reason, however, was simple fascination. I wanted to know how a five-person a cappella group, one that relies on insanely tight harmonies and arrangements, would fare in an outdoor festival environment, not exactly a place where perfectly tuned mixing and ideal audio conditions are common.

Would they be able to keep those tight harmonies? Would their music be lost, buried underneath the rest of Summerfest’s noise? And am I going to be able to see them through this Stephen King-like misty fog that’s squatted on top of Milwaukee for the past week?

As it turns out, I and the massive, ecstatic young crowd gathered at the Briggs & Stratton Big Backyard Thursday night had nothing to worry about, as the incredibly talented quintet put on a complete show of totally in-tune entertainment. Indoors or outdoors, sun or mist, there seems to be little to stop Pentatonix’s climb to the top of the a cappella world – and possibly the pop world.

The group opened with its Daft Punk medley, one of several YouTube covers to go viral for the Texas-based singers. The mix was a little on the bass heavy side, though I was very close to a stage speaker, which may have distorted my personal take. When I went further back a song later, it seemed as though the audio leveled out perfectly and stayed that way for the rest of the night. Even with the bass on high, though, the unique and unpredictable arrangement still stood out, and the band’s choreography sells a song well, energetically bounding and dancing all across the stage.

Pentatonix continued on into one of its few original songs, "Hey Momma" with a brief appearance by "Hit the Road Jack," and "Telephone," which main vocalist Scott Hoying informed the crowd was the first song the group performed together. In both cases, the complex, complicated arrangements came through almost perfectly with very little lost in the open festival setting. Instead, there was merely plenty to marvel at, whether it be bassist Avi Kaplan’s bottom-of-the-ocean deep bass, tenor Mitch Grassi’s explosive yet crystal clear falsetto or beatboxer Kevin Olusola’s insane, seemingly inhuman vocal percussion.

Covers of "Video Killed the Radio Star," seemingly Beyonce’s entire catalogue on turbo (complete with Kaplan singing a brief verse from "Bootylicious," predictably sending the crowd nuts) and "I Need Your Love" soon followed, with the night mist creeping up onto the stage. Calling the tunes merely covers, however, feels like selling Pentatonix short. Each song is recognizable, yet also wholly original and unpredictable. When the band wrapped up the show with "Can’t Hold Us" and an encore of "Thrift Shop" and "We Are Young," it was as though you were hooked on the hits all over again – even after their mind-drubbingly omnipresent radio airplay rendered those songs almost unlistenable.

Much like their first Milwaukee visit, the middle of the show was a kind of talent show-and-tell. Hoying told charming stories of how the group came together (including a fun fact about searching YouTube for beatboxers and an impression of Kaplan that sounded more like Dr. Claw from "Inspector Gadget"). And speaking of Kaplan, the man is clearly the fan favorite. Considering his voice is like blankets dipped in chocolate for the ears, the love is understandable. It seems the appreciation is returned as well, since Kaplan couldn’t stop saying, "I really like you guys a lot" throughout the evening.

The band, as a whole, was pleasantly chatty – even dropping the tidbit that they'll be appearing in the upcoming "Pitch Perfect 2."

After Kaplan briefly performed some overtone singing, remarkably producing two notes at the same time, he handed the stage over to Olusola, who showed off his simultaneous cello/beatboxing chops – a skill on display in a recent Coke ad – with an original song, "Renegade," that he wrote. The crowd was deathly quiet – and luckily, so was the rest of Summerfest other than a little loose sound coming from the show over at the Harley-Davidson Roadhouse – certainly more bedazzled than bored. 

Pentatonix went into the home stretch after that, cranking out terrific, surprisingly full renditions of "Say Something" featuring Olusola on cello, "Natural Disaster" (an original song, complete with an audience sing-a-long component that was too complex for this has-been college a cappella benchwarmer), Imogen Heap’s "Aha!," the evolution of music, "Royals" and a smooth groovin’ version of "Let’s Get It On," playfully sung as is tradition to a girl from the crowd brought on stage. Kaplan sat on her lap; swoons and screams predictably ensued.

When the 80-minute set came to a close, time seemed to have flown. It was such a light, loose performance that it would be easy to take what Pentatonix just did – uniting simply five people’s voices and creating a full sound that filled an outdoor festival stage without sacrificing the harmonies and unique twists that make their music above and beyond the rest of a cappella – for granted.

During "Say Something," the combination of the stage lights and the creeping fog almost gave some band members a heavenly glow. Considering the show they just put on, it fit.