Cline, the preposterously skillful and adaptable guitarist’s guitarist, is known mostly for his nasty solos with Wilco. But he's also part of the underground rock and free-jazz scenes, in which he's made challenging and expressive music with countless musicians, including those in The Nels Cline Singers. Cline's short set in the NPR Music offices serves as a rare and intimate master class from a thoughtful musician.