Two copyrights, one song
When people say "I own my music," they often mean two different things at once. Under U.S. copyright practice, a sound recording and a musical composition are separate works. The U.S. Copyright Office is clear: a copyright in a sound recording is not the same as, or a substitute for, copyright in the underlying musical composition.
That distinction is the whole ballgame for independent artists. Master rights and publishing rights can travel on different contracts, pay through different channels, and get sold or licensed by different parties.