The Copyright Act of 1976 states that a copyright is created for a work if it is an original work and fixed in any tangible medium of expression. A copyright exists the moment such a work is created. However, many people choose to go an extra step and register the copyright, which can help put others on notice that you are the owner of the copyright.
In order for a work to be original, it must be your own independent creation. No proof of originality is needed in order to register your work with the Copyright Office. However, if an infringement suit is brought against you later, proof of originality will be examined at that time. In the case of music, courts typically look at the similarity of the beat, rhythm, lyrics, and harmony.
Tangible Medium Requirement
A copyright only protects works that have already been created -- not, for example, just an idea you have for a musical project. In the case of music, it must have been recorded or written down in some tangible form that can be perceived, reproduced, or otherwise communicated either directly or with aid of a machine or device. In other words, the music must be put in a form which others can see, read, or play on some device. In order to register the copyright, a copy of the recording or sheet music is typically required.
The owner of a copyright is given basic exclusive rights, which include the right to copy, the right to derive, the right to distribute, the right to perform, the right to display and the right to digitally transmit. If anyone violates these rights, you can bring a copyright infringement suit in federal court. There are also criminal laws that protect intentional copyright infringement. Even though a copyright exists the moment a work is created and placed in a tangible medium, it is necessary to register with the Copyright Office if you ever wish to file a lawsuit against someone for infringement.
Musical Copyright Proof
If an infringement suit is brought, the court will look at various types of proof to determine whether the copyright is valid and whether the other person infringed your copyright. At that time, you need to provide proof of when the music was created and recorded. The owner that registered first is generally presumed to have created it first. However, proof like a digital recording showing the date it was created or a publication date can rebut this presumption. Expert witnesses may be needed to determine the differences in tempo, rhythm, and harmony of each work. If the music is found to be substantially similar to another work, infringement has generally occurred.