Robert Plant is known for his voice, but that's not why The North Mississippi All Stars asked him to be on their next album.

Plant joined the band last week at Royal Studios in Memphis to add harmonica to two songs. Studio owner Boo Mitchell says, "It was unexpected. We let him use Al Green's mic. He dug the sound and the fact that we haven't changed anything. He had a fabulous time." But it got off to a rocky start after Plant dropped his harmonica in Indian incense and needed another one. Mitchell adds, "He should play harmonica more than he does. He is a bad-ass harmonica player."

Plant became friends with the All Stars after they opened a few shows for him.

The North Mississippi All Stars will headline Sioux Falls JazzFest Friday (July 19)