This app is a work around for a bug in some Galaxy brand devices that causes some audio to bypass music visualizers.
Audio tunneling is a feature that can reduce battery use while playing music, but it has a bug that causes tunneled audio to bypass music visualizers.
This app runs a persistent service with a silent audio player that attempts to occupy the audio tunneling feature, so media players won't attempt to use it. The service itself does not use any noticeable amount of battery: it simply opens a blank audio file and pauses it.
Tunnel Blocker includes a built-in visualizer so you can see if it's working. For convenience, it has two buttons that can be used as shortcuts to your favorite music player or visualizer.
Many thanks to h6a_h4i for finding a workaround for this problem. Check out h6a_h4i's app, Music Visualizer!