Well I thought frequency and/or amplitude or one of their games created the notes based off of sound(so you could play any song).
That's why I was unsure of how they were working this and asked the question. Even still if it's based on existing charts, I wonder if they'd double up or just cut things out when missing.
And obviously no matter the method they used, yes I know it'd be impossible(for regular users) to play their own songs(things like mp3s) either way.











