As well-known in their native Pakistan as their peer, Eddie Vedder collaborator Nusrat Fateh Ali Khan, Shafqat Ali Khan and his father, Salamat Ali Khan, perform Hindustani classical music. Like traditional sitar music, this involves sinuous improvisation on established themes, rich, hypnotic drones, and awe-inspiring technique. Joined by tabla player Samir Chatterjee, the duo performs at 7:30 p.m. on the steps of the Freer Gallery, 12th & Jefferson Dr. SW. FREE. (202) 357-3200. (MJ)