Marc Lempert is the director of the feature-length documentary Pocket Full of Soul, a "comprehensive exploration of the culture, the players, the politics, and of course the music" associated with the harmonica. He and the producers of the film are offering special free screenings on World Harmonica Day, April 18. We talk about what it was like interviewing the numerous star players, learning about the instrument and its community, and his personal transformation in making the movie.