I have an MP3 that is fan-based audio commentary. The commentary was not mixed with the actual audio from the original television episode. I would like to mix the fan-based commentary with the original audio. But it would be nice if the original audio came through at normal volume when the commentary audio is silent, and have the original audio at a reduced volume when the commentary audio is not silent. It would be preferred that this volume adjustments are automatic.
Do you have any recommendations? I have no audio engineering skills, so I need a rather simple procedure.