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oh, nevermind.... it is just "../"

I'm pretty sure the answer to my question is well documented, but I never found the right way to phrase it when searching...
Up until now, I've only had to reference files located in subfolders...

To use that to mute your sound, put that code inside of a function called by an mouse-click eventlistener attatched to your button....

muteVol_btn.addEventListener(MouseEvent.CLICK, muteVolume);
...