The fifth part of London's Southbank Centre's Rest is Noise festival - that takes as its starting point Alex Ross's survey of 20th century music - focuses on music in pre-war America. Here, US conductor Marin Alsop and the Guardian's Tom Service discuss the African-American inspiration for Antonín Dvořák's New World Symphony, and key figures from the era such as black composer William Grant Still, and Duke Ellington's mentor, violinist Will Marion Cook.

Laura Barton finds out about London's Southbank Centre's year-long music festival that takes as its starting point Alex Ross's book on the classical music of the 20th century