Masters vs. Demos,
and which is right for you
Demo Recordings
Demo recordings of your song are not publicly released. Instead, they are used to convey your idea. That is, to demonstrate your song to publishers and/or artists.
Demo recordings need a FormPA copyright to protect your intellectual property.
Demo recordings do not require a FormSR since they are not publicly released.
Master Recordings
A master recording is the final version of your song that will be publicly released—as such, further legal protections are necessary.
Similarly to demos, a master requires a FormPA copyright to protect your intellectual property.
The difference is that you must additionally file a FormSR, and do so within one year of its public availability to retain rights to the master. Should you fail to do so, the recording will fall into the Public Domain. After which, it will be free to use by anyone, anywhere. Note that for a song to be "Radio Ready" you need more than just a FormPA and FormSR.
Radio Ready, the legal stuff
To have a master is one thing, but to be ready for public release requires a little more. To make your song truly "Radio Ready" you must retain written contracts; from each performer—giving you permission to use their performance in your master recording; from the producer, publisher, and others—defining any percentage of royalties owed to them; and from anyone else involved in the production that can claim rights to the master. If you do not acquire these contracts before releasing your song, you are at risk of legal repercussions. Always review all contracts with an attorney to ensure their legality.
Performing Rights Organizations
In addition to the contracts, you should join a Performing Rights Organization (PRO). Some examples in the U.S. are ASCAP, BMI, and SESAC.
PRO's act as an intermediary between you and the End Use of your music—radio stations, venues, TV, etc. They collect licensing fees from the End Use and distribute royalties to you from those fees.