This isn't true. Replaying public domain music through mechanical means adds no creativity to the work, and thus has no copyrightable elements.

For reference: this was specified in article 14 of the new EU copyright directive. One of the few good changes in it: https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CEL...

The type and timbre of the instrument used, the speed and volume of playback, any post-processing decisions, etc. are all creative choices and thus can make a resulting work copyrightable.

Be careful using generic music from the Internet.

Yes you are correct. The audio recording any person generates through the procedure I outlined above is now copyrighted by that person, who may then choose to place it in the public domain.

It's like if I recorded myself playing Für Elise. The recording I generate is owned by me, unless I release it to the public domain.

Yes, but then you as an author can choose to place your own performance in the public domain.

I thought that wasn't clearly established. I believe the assumption has been that you could call something public domain, and obviously people do so, but I don't believe it has been tested in court.

Not that I can see an obvious reason why it would be so tested, and frankly these are fuzzy memories from 15-20 years ago.

To what extent it is obvious just a simple statement that something is public domain would work depends on jurisdiction, which is why things like CC0 [1] exists.

[1] https://creativecommons.org/publicdomain/zero/1.0/legalcode