Pentatonix, 7 p.m. Aug. 31, Fairgrounds Grandstand. Pentatonicx is an American a cappella group founded in Arlington, Tex. in 2011. The group is: Scott Hoying, Mitch Grassi, Kirstin Maldonado, Kevin Olusola, and Matt Sallee. Pentatonix won the third season of NBC’s “The Sing-Off.” The group has sold 10 million albums worldwide and released 12 studio albums, from “PTX Volume 1” (2012) to “Holidays Around the World” (2022). “That’s Christmas to Me” (2014) was the highest-charting holiday album since 1962. Pentatonix is named after the pentatonic scale, a musical scale with five notes per octave, representing the group’s five members. Their singing style is that of pop arrangements with vocal harmonies, scat-singing, vocal percussion and beatboxing. They sing cover versions of pop songs, Christmas songs and original material. The group has performed at The White House, “Macy’s Thanksgiving Day Parade” and The Hollywood Bowl. Pentatonix was in season nine of “The Masked Singer” as “California Roll” in 2023. It’s the second time that Pentatonix headlines the Allentown Fair’s Grandstand. They performed to a sold-out crowd at the 2017 Allentown Fair.