See the Music

Record grooves under an electron microscope

It has CD pips, too, for those of you too young to remember what a “record” is.

But if you put a needle in the groove and moved them relative to each other, the needle would wiggle back and forth. Use a transducer to convert it to an electrical signal, amplify it and send it to a speaker (which would essentially do the reverse). The groove is a composite of all the waveforms of the song, added together.