Billy Strings captivated a sold-out Georgia Theatre audience on Saturday night, not with theatrics or fancy lights, but in the way each musician shredded his instrument. The Nashville-based string band performed back-to-back bluegrass jam sets standing in a line on thin carpet and a completely undecorated stage. But the audience didn’t care. Their enthusiasm grew as each member of the band showed off his skills with his instrument. Audience members seemed either intent on recording the 10-minute-plus jams or bopping along to twanging of the string instruments. The band is currently on a nationwide tour and will release a new album, titled “Home” at the end of September.