Any experience with writing software to alter audio output?

Answer 1

Don't know of any, but it will no doubt be a low level programming. C, C++. If you can write efficiently in them, you might want to look into the code base of VLC media player since it open source and if that is kind of hard, I believe you can find audio manipulation libraries on git hub. It could be written in C or C++, but could be ported to JS or have JS api for easier interfacing. Regards...