Try to go to the 'General' tab in the Wallpaper Engine settings and change the 'audio input device' around and see if any of the audio input devices start working (obviously you probably don't want it to react to your microphone, though). If that does not react to sounds played on your computer, there may be something wrong with your Wallpaper Engine settings. To make sure there is nothing wrong with your wallpaper, try using a popular audio responsive wallpaper like this one: Usually it should just work out of the box. Due to how sound recording works, it's actually not possible to differentiate between programs, so Wallpaper Engine will always react to any sound played from any program. What the other user meant by 'system' is that Wallpaper Engine will react to ANY sound played on your system from any program.
