The Band of Desperate Men — Britt Dean, Doug Oster and Clay Spurz — will perform their blend of pure and simple harmony Oct. 13 at the Sautee Nacoochee Center. The group sings in many styles mostly from the American roots rainbow of music: country, old-fashioned rock ‘n’ roll, bluegrass, folk, pop, doo-wop and blues. They also venture outside the American stylebook, with a ballad in Spanish and an a cappella doo-wop song in Chinese.