The Robert Mann Chamber Music Series continues with a spotlight on the Festival’s own musicians. Haydn’s String Quartets achieved a new range of expression for secular music; his String Quartet C major, Op. 20, No. 2 is a diamond from start to finish. Debussy, a master of impressionism and fantasy, creates a quintessential dreamscape in his Sonata for Flute, Harp, and Viola. Instead of treating his string octet as two individual quartets, Mendelssohn’s innovative Octet finds all eight musicians working tightly together in, as the composer requested, “symphonic orchestral style.”