...Once you’ve determined who owns the publishing and the master, you must contact them separately and ask for permission to use the song. This can get tricky when there are a lot of songwriters involved. Katy Perry’s song "California Gurls," for instance, has five publishers. Therefore, if you wanted to clear this tune you would need approval from all five of the writers and on top of that you would need approval from Katy Perry. If one of them says no, then unfortunately you can't use the song...