Of all the things that give musicians anxiety dreams, the master class has to be up there at the top. Out on stage alone, not only performing for an audience, but having a master teacher there to stop you and critique everything you're doing. And yet, it's a marvelous learning experience, both for the student and for the audience. Cellist David Finckel and pianist Wu Han give a master class on (what else?) cello and piano sonatas, at the Aspen Festival. Following that, we'll hear them perform a Beethoven cello sonata, from a concert at Aspen last month. Plus, violinist Julia Fischer gives a spectacular performance of a Bach solo violin partita in Aspen.