Here's a relevant answer from another similar thread --
Just let us know at what part you need help to understand, and --
Nope, you don't want that setup for background-music/BGM [unless you want to go back to 40/50's, hahah].
Mono channel at 22050Hz is only for sound-effects/SFX. With BGM you'll always want it as Stereo channel at 44100Hz.
P.S. Be advised that all of this was written with GOG version in mind. I'm not sure about the others though.