In this interview, Yannick Nézet-Séguin, conductor of the Philadelphia Orchestra, discusses Tod Machover’s “Philadelphia Voices,” a work commissioned for 2018. The orchestra is featuring American composers during its 2017-2018 season. Other works included the Bernstein Centenary featuring “West Side Story,” “Chichester Psalms,” and Symphony No. 2 for Piano and Orchestra (“The Age of Anxiety”); Wynton Marsalis’s Violin Concerto; and Michael Tilson Thomas’s “Four Preludes on Playthings of the Wind.”