[seandougall]

You can generally only copyright the parts you change. Sort of like how Disney can copyright their version of Rapunzel, but they don’t own the fairy tale.

(Edit: that’s assuming you’re asking about a derivative work, which I may have misunderstood)

[itronitron]

I guess my question is more focused on whether a person can copyright something they created that was created by something else previously. So, if a musician creates a melody and then later finds that same melody was previously recorded on an album from the 1990's can they still copyright their melody? Does it matter whether the 1990's recording was machine-generated melodies or human-generated ones?

[singron]

This is discussed in the video somewhat. Copyright allows parallel invention. E.g. 2 people can copyright the same thing as long as neither one copied the other. In the video, they claim this is usually difficult to prove in court if the first work had at least moderate notoriety before the second was produced.