You've heard about Bach, Beethoven and Mozart. But how about Carrillo, Maceda and Ustvolskaya ? In her new book, Sound Within Sound, writer and BBC presenter Kate Molleson tells the stories of 20th century composers whose work was groundbreaking, but who are underrepresented in history because what they made didn't sound like "traditional" classical music. Though conversations around race, gender, diversity, and classical music have seen progress in recent years, Molleson tells Talia Schlanger that there is still a significant gap in the canon when it comes to recognizing many of the trailblazing composers outside Europe and the United States.