system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do earphones separate sound in vertical space?

I listen to a lot of binaural recordings, and it's amazing how they can make you feel like sound is coming from above, below, in front, or behind you.  How is that possible?  I understand how left and right work, and to a lesser extent I even understand how front and back work, but how does up and down work?
gpt
There are a couple of reasons that we can hear what direction a sound is coming from:

•Left to right is the simplest, we can pick up the slight delay from the sound taking a little longer to get to one of our ears and figure it out from there

•The other directions are because of the unusual shape of our ears - in getting to the eardrum the sound will bounce around in various different ways depending on where the sound is coming from, and our brains have had so much practice at listening to those echoes that it knows exactly what direction just from that exact echo.

Binaural recordings are literally just recording the exact sound that gets to your eardrum, and so it tricks your brain into thinking that it echoed off your ear to have come from that exact spot instead of coming from your headphones.