If you wish to submit something in the public domain, it must not be the original sound recording but, a re-created cover. You cannot re-release the original work "as-is."
When a song enters public domain
In the U.S., any musical works published before 1922, in addition to those voluntarily placed in public domain, exist in the public domain. In most other countries, music generally enters the public domain in a period of fifty to seventy-five years after the artists' death. (Public domain rights must be verified for each individual country.) It is important to note the distinction between "musical works" (sheet music and other compositions) and "sound recordings" (audio files, CDs, records). Virtually all sound recordings will not fall into public domain until 2067, unless explicitly placed into the public domain by its creators or made by an employee or officer of the United States Government acting under their official duty.
Generally, published works from 1922 and earlier are in the public domain. Unpublished works are protected for the life of the author plus 70 years. Most sound recordings, however, are not currently in the public domain regardless of year. In some cases, more recent works may be in the public domain if the author never obtained a copyright. Sometimes the author deliberately dedicates the work to the public domain. In that case, the work will have a notification that says “This work is dedicated to the public domain,” or similar notation. There are many exceptions and renewals available to copyright holders, so you should not assume that a work you wish to use is in the public domain.
Copyrighting works based on public domain
Derivative works that have been re-created using public domain works can be copyrighted if a sufficient amount of creativity has been added to the work. We recommend seeking legal advice to determine your rights as to each work. It is not possible to directly own a work that is in the public domain.
How to determine if a song is in public domain
Resources such as http://www.pdinfo.com, or US Copyright Office at www.copyright.gov are helpful, but not the only, resources to determine whether a work may be in the public domain or is protected by copyright.