Today, “American Idol” is the country’s biggest music star-maker, but decades ago, the Golden Age of Radio fulfilled the idol-making role in the U.S. Feinstein traces the phenomenon with archival clips of Bing Crosby, Cab Calloway, Kate Smith and many others. He visits with TV and stage star Rose Marie (best known as “Sally Rogers” on “The Dick Van Dyke Show”) and learns about her career as a highly paid child radio star named “Baby” Rose Marie. On his own NPR program, Feinstein showcases the virtuoso talents of classical superstars, including violinist Joshua Bell and pianist Jeremy Denk. Finally, he discovers a lost radio program that featured Rosemary Clooney, and recalls his own memorable duet with her.