system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do noise-cancelling headphones actually block out 99.9% of all outside noise, even though they seemingly are structured the same way as regular headphones?
gpt
If you take a waveform and inverse it, then play it along with the original, they'll cancel each other out (+1 combined with -1 equals 0). Noise canceling headphones actually have a little microphone on the outside that it uses to listen to the noise around you, and then it produces the inverse of that noise and plays it through the headphones, negating much of the noise outside.