Jeremy Denk played Mozart at Carnegie Hall Wednesday with the San Francisco Symphony. Eric Thayer for NPR Music hide caption

itoggle caption Eric Thayer for NPR Music

This rare portrait of Bach, by Elias Gottlob Haussmann, hung in John Eliot Gardiner's home during World War II. courtesy of William H. Scheide, Princeton, N.J. hide caption

itoggle caption courtesy of William H. Scheide, Princeton, N.J.

Jeremy Denk's new recording of Bach's Goldberg Variations comes out Sept. 30. Michael Wilson/Courtesy of the artist hide caption

itoggle caption Michael Wilson/Courtesy of the artist