Simply reloads minecraft's sound system. I made this before I realized F3+T could be used to reload all resources (Resource Pack, for example) but as that is extremely slow (Like changing a resource pack slow) I decided to publish this anyway. By default it binds to the 'P' key, but it remaps like any other key.
On Windows it resets to the systems default sound device, without restarting MC/reloading resources. Not quite sure if it works the same on Mac/Linux. Be happy to test it out if requested, or add a check to make sure it doesn't crash there (Although it shouldn't as far as I know).
Enjoy!