analog signal to your speakers, so you can listen to it. The program receives the input from the scanner, it converts it from digital to analog. I forget where I saw it at, at the time I didn't care because no one around me was using it(I work for the county), now the city is in the process of switching, the county to my north as switched, and the city to my south has switched, at some point I'll end up buying a NX-800, but I just don't have $700 sitting around right now.