When one hears a police siren, music, and a car alarm all at once, how can these multiple types of vibrations be accommodated by the medium? (Let's take the simple case of the diatomic gases in air.) Is it possible for individual molecules to vibrate and propagate multiple sound waves at once, or do different groups of molecules somehow end up carrying a certain sound, while other groups carry the other sound? Do they "trade roles" quickly? Is oxygen more apt to carry certain types of sounds than nitrogen? In the case of one sound, do all/most molecules vibrate to propagate the sound, or only a small amount? Thank you for your wisdom!