Well, you can certainly create something as copyright free -- but most of the time, though, this doesn't apply to free, downloadable sheet music.
Most sheet music was published -- and had a copyright registered at time of publication. You actually don't need to register a work in order for it to be copyrighted -- but protecting your copyright is a lot easier if it's registered.Once registered, the copyright doesn't last forever. Recently (in the United States) a copyright lasted 75 years after registration. An item published in 1920 became public domain in 1995.
Something happened in 1998, though. The "Sonny Bono Copyright Term Extension Act" extended that copyright period for a still to be determined number of years. So, if an item was published prior to 1923, it's now public domain. If published after 1923, it's still copyrighted.
And it's all because of Mickey Mouse. Mickey, you see, was copyrighted in 1923. If allowed to pass into the public domain like the prior law allowed, it could have caused the Disney corporation no end of grief. The whole intent of the 75 year expiration period was that an item would have passed out of public interest after 75 years. No one had thought about fictional characters who's appeal spanned generations.
So, because of Mickey Mouse, nothing since 1923 has passed into the public domain. The Sonny Bono act (also known as the "Mickey Mouse Act") doesn't really address when Mickey's copyright will expire; it just postpones the determination date until later. Perhaps Congress will allow Mickey -- and everything else whose copyright would have orginarily expired -- to become public domain down the road. But ... I wouldn't bet on it!
