Thanks to user K1CHWA for answering my question.
STEP 1) Create a folder inside your addons folder within your directory for which you will store the sound files you want to verify.
(located: Program Files/steam/steamapps/common/left 4 dead 2/left4dead2/addons)
STEP 2) Insert your addoninfo.txt and sound files into your folder for where they are located
(example: sound/music/pzattack; pzattack being the folder containing your files)
(addoninfofile example here: http://developer.valvesoftware.com/wiki/Deadline_ AddonInfo_ File) remove the spaces
(place addoninfofile into your addon file folder next to sound)
STEP 3) Go into your Left 4 Dead game and open your console.
(open console using the [~] key)
(to activate console go from the main menu: Options] Keyboard/Mouse] Allow Developer Console: Enabled)
STEP 4) Type in: snd_buildsoundcachefordirectory addons/[insertnamehere]/sound
(be sure to replace [insertnamehere] with your addon folder name)