Before you go any further, put in your headphones and press play on this horrifying version of Mariah Carey's "All I Want for Christmas Is You".
Earlier this week, Tumblr user formeldeharv converted Carey's Christmas hit from an MP3 to a MIDI file, then back to an MP3, and posted the result online.
But the thing is: You shouldn't be able to hear Mariah Carey's voice, because it's not actually there.
A MIDI file shouldn't be able to hold enough information to encode the complexities of a human voice.
Another Tumblr user reblogged the song, commenting:
I'm driving myself up the wall because I swear I can hear the vocal line but I don't know how that could be if it was truly converted to MIDI. Unless you can replicate speech sounds entirely with modulated MIDI notes, in which case I'm actually impressed with this tire fire of an MP3.
Now for the ~science bit~.
"Our auditory perception is very good at 'filling in' missing information, especially if we have some knowledge or expectations about what we're listening to," Professor Bill Macken, a psychology professor at Cardiff University told BuzzFeed News. This is called "top-down processing".
"Given that people are so familiar with the song, just a tiny bit of the signal remaining is enough for our brains to reconstruct things so that we perceive the voice."
Basically, you know the song already, so your brain fills in the gaps and tricks you into thinking you heard the song, when in fact you didn't.
Macken says this isn't just our brains "playing tricks on us", it's our brains trying to figure out what's going on there based on incomplete information.
"The fact that under 'normal' circumstances we don't notice this happening just shows how well tuned our perceptual systems are to picking up and using any available information in order to make sense of the world, rather than showing how easily tricked they are," he says.