Actually, this can be more complicated than it seems at first. It used to be, like Sharmy said, that after 75 years that the piece was first published or performed in public (not written) for the first time, IF IT WAS PUBLISHED IN THE U.S.A., it would become public domain. This all changed in 1998 (if the memory doesn\'t fail me), and copyright terms have been extended notably. So, in general, if something was published in the U.S.A. first, and this happened in 1922 or earlier, then it should be public domain.
To complicate matters, if the piece was published in other countries, the rules for that country apply. I remember reading that works by Debussy and Ravel published well prior to 1922 are still not in the public domain, and that the French government intends this to remain like that.
Don\'t take my word as the truth, but do yourself a favour and do some independent research on it.
I\'m no expert in copyright, but here is some additional information. This may further complicate matters. Please seek professional legal/copyright search services if required.
Of course, much \"classical\" music is in PD. You need to find the date of the first publication.
Publishers of folk songs, education texts, and others will take a PD song and then republish it with a new copyright date. The trick is that they make changes to the music itself, the lyrics, whatever. Thus, they now own the copyright of their version of the PD song.
If you are using the exact version of that new copyright, you are using a copyrighted version of the song and are then required to get publications permissions, pay fees, etc. If you use most of the PD version but used my copyrighted revised lyrics you will need to get permissions.
To use a PD song/composition, you need to find the original source notation and publication date to confirm that it is in PD.
I am not certain if classical music publishing does this as well. I am fairly certain they do. They want to protect what they are currently publishing and thus copyright it.
Research is required.
In classical music, if you find the \"urtext\" or original notation by the composer, then technically that SHOULD BE be in the PD domain if you satisfy the expired time limit.
If you want to use a theme, you should find 3 published versions of it that are identical. This is a clue that the material may be PD. However, one of the publishers could have paid a prior publisher for the exact use of their material. You might contact the publisher, and ask for the copyright owner. Sometimes the publisher says the source was PD.
In folk music, you might need to find 3 sources of a song in Public Domain to confirm that a song is in PD. (I am not certain what the legal requirements of proving PD are).
Disclaimer. Seek professional legal advice. But the song/music research is what will determine PD.
If you deal with the US Copyright Office, even they will have a disclaimer saying that they cannot verify or confirm if a song is PD.
All I know is that the person putting out the material is responsible for being compliant with either PD verfication, or by seeking copyright permissions.
If this were a commercial/broadcasting/recording release, I would consider a firm that does copyright searches. I do not know of these personally.