The idea behind David Isay’s StoryCorps is simple: interviews are conducted with ordinary Americans from across the country, recorded, then broadcast on the radio documentary program. Isay’s new book, Listening is an Act of Love, compiles some of the most memorable stories from the program. Tonight at 7 p.m., Isay gives a talk about the book at the Milwaukee Public Library, which incidentally houses a StoryCorps recording station.