The notepad will tell you everything, When you open sound4 with HXD, hit search, go to, type in the last few numbers and letters that come after the 0. You didn't see what it was because I didn't type it, i pasted it which it tells you to do in the video right before hand.
no your new file isn't sound4.pak.bak, this is you're back-up file or what the file was before it was modded. Whever the sound4.pak was that you opened with HXD, hopefully on desktop like i said, is what your new sound4.pak is, It isn't that bad you can always repatch the game or you could just delete sound4.pak.back from DBO pack folder and put the right sound4.pak into there.
(You should keep created folder in case you want to mod different sounds)
Is there anyway that you can send me music with skype xD or something i tell you music you create me moded file for title in dbo i mean when you logg in! :)