On this week's GPB broadcast, frequent guest Roberto Abbado conducts the Atlanta Symphony. Soprano Heidi Grant Murphy soloes in both Samuel Barber's nostalgic Knoxville: Summer of 1915 and Mahler's heaven-bound Symphony No. 4. And pianist John O'Conor steps in on short notice to perform Mozart's fifteenth piano concerto. As Roberto Abbado tells us, themes of childhood and innocence and heaven run through the program.