That's J.S. Bach's Canon a 2 per tonos you're hearing. (If you have clicked on the little speaker icon, that is.) It is only due to modern advances in sound synthesis and psychoacoustics that we are able to hear it presented this way, both solved and endlessly repeatable. If you don't know what I mean by that then listen for the key changes.
If the implication was not clear, I plan on making some music someday and including relevant information about it here. Whether that plan goes anywhere or whether this site will continue to promote nothing of particular value is an open question.