Rob Rapley is writer/producer/director for the American Experience documentary film "Voice of Freedom" that airs tonight on Milwaukee PBS channel 10 and on PBS stations across the country. The film explores the story of the historic concert sung by African-American contralto Marian Anderson on the steps of the Lincoln Memorial on April 9, 1939, after she was not allowed by the D.A.R. to sing a benefit concert in Constitution Hall because of her race.