Phil Hartup shows how you can expand the PC version of Guitar Hero 3 by adding your own MP3s to the game
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You might start by adding tracks one at a time, but once you're used to the procedure, you can add songs in bulk. To do this you need to assign a folder into which you’ll put the songs to be imported. For the mass importer to work you need to place each track mp3 and its corresponding chart file into its own folder, the program will skim down one level through the subdirectories within the selected folder, pick up the mp3s and pair them up with the charts. The control panel automatically names the track using the same name you used for the folder. You'll still need to manually set the track information for use in the actual game.
The range of options available using the Guitar Hero Three Control Panel isn't just limited to adding songs that you like to the list. You can for example add entirely new tiers to the game, so all your custom tracks are in one tier and the existing ones are kept safely in another.
Even more useful for users on slightly slower PCs are the speed boost options, which essentially cut out some of the unnecessary graphical fluff, to leave you with the bare bones and a better frame rate.
With any luck, you should now be able to add any song you like to Guitar Hero 3. Invite your friends around for a jamming session with all your favorite tunes, or make a romantic evening just a bit more special by mashing a plastic guitar with your other half.