Best practices for uploading a track in the public domain
Let’s start by busting a myth. The vast majority of the material that is publicly available on the internet for free is NOT in the public domain. If you want to create something new based on publicly available material, it is your responsibility to find out whether the material you want to use falls in the public domain before making use of it. It is absolutely essential that you verify this, even if you are using someone else’s material for promotional purposes only or if you are not making any profit from its use.
Works that are in the public domain either fell out of copyright protection or are not eligible for copyright protection - such as federal government works in the US territory - or were gifted to the public domain by their creators. This type of works can be used without requesting permission from their creators. For any other work that does not fall in the public domain, you will certainly need the permission from the copyright holder(s) to do so.
What’s important to bear in mind is that copyright protection can vary from country to country and that when a track is uploaded to your account, it is available everywhere in the world. You should therefore make sure that the material you want to use has fallen in the public domain globally.