Audacity
Audacity is a free sound, music editor and creator. It is extremly easy to use and learn.

Download
http://www.audacityteam.org/download/windows/

Left 4 Dead 2 Authoring Tools
You will need this to publish the addon if you plan to add it to the workshop.

Download
To download this, go into the tools section of your steam library. Simply search the list until you find it and install it.

Create a folder on your desktop with the name of your addon. I am changing the Tank music to the Pokemon: Firered & Leafgreen champion music. (Dont judge me). So i will name my folder
champion tank music so that i know what it is. (Name your whatever you want)

All the files for music are not hiding in some crummy .vtf or .vmf. Most of them are .mp3 files so we dont need any special programs to get them. All we have to do is find them.

Disclaimer:
I wont show you the location of every sound file. It can all be found if you take a few minutes to search for it.

The location of the music files.
C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\sound
You will have to search through the folders until you find the files you want. I am making a tank music mod so i will need to be here:

C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\sound\music\tank

Do not close your file explorer or whatever you use, we need the directory locations sill.

create folders that match the sound files directory. Mine looks like this:








To make it even simpler inside the folder, copy the file directory starting from the "sound" folder.
Ex. sound > music > tank

Copy the files over from the main directory to your addons folder.










Open Audacity. Go to import > audio and find the music file you want.

Dont have a music file?
Try using this tool if you dont have one, its straight forward to use so i wont explain it.
https://www.onlinevideoconverter.com/mp3-converter

Once you Import the music you want, Import the music or sounds from the game that you want from your addon folder. Mute that track. It should look like this:











Crop your music to match the music from the game.














Export the file into your addons folder. A prompt will ask you if you want to overwrite this data. Click yes. Do this for every file you want to change. Make sure it is named the same as the file you wish to replace.

You will need to create a VPK shortcut on you desktop.

Find the VPK file in this directory
C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\bin

Once you do that drag your addons folder into it. A little file with the name of your addons folder should appear on your desktop.











Open Left 4 Dead 2 Authoring Tools. Click workshop manager. Then click the plus sign. Drag the VPK file into the file section and fill out the rest of the data. Your addon is ready to be published!

If your addon does not work, run this checklist:

Did you spell all of the file directory folders correct?
Are any conflicting addons enabled in-game?
Did you upload the correct file?

If your still not sure leave a comment on this guide!