Founded in 2013 on the initiative of Carnegie Hall, the National Youth Orchestra of the USA honors the venerable ideal of America as a melting pot. Top-flight Black, white, Asian, and Hispanic musicians between the ages of 16 and 19 band together under the world’s preeminent maestros to explore the most challenging scores in the repertoire. This year’s selections: Mahler’s Fifth Symphony and Elgar’s Cello Concerto, with the grandiloquent Alisa Weilerstein as soloist. —Matthew Gurewitsch