There was a time not too long ago that if I saw a band without a drummer, it was incomplete. I used to feel that there were duos, trio, quartets, and so on, but they weren’t bands until somebody was pounding something with sticks. I say this now because 1) I’ve obviously grown up a little and 2) bands like the one backing up singer Corey Harris is on the blues fringe, as well giving a bit of a world beat twist to his standard trio. It was like Delta in the desert. Harris picks like Lightning (Hopkins, that is) but allows the music to swirl and swell and hypnotize as he did last night in the Big Tent.