The Concord Sonata, which many consider Ives’s masterwork, is a deep, labyrinthine collage of American folklore pinned around endless reimaginations of the opening four notes of Beethoven’s Fifth Symphony. His Piano Sonata No. 1 is a rowdy and rude piece, packed with jittery ragtime energy and with brief moments of exquisite repose—Denk’s performances are graceful and thoughtful. The Violin Sonatas are rarely heard in comparison, but rehearse many of the same preoccupations—Ives’s nostalgia for old America in conversation with his fascination for the New World and all its possibilities.