ANC headphones report background sound with microphones and invert its section applying created-in electronics. Then they Perform the inverted/opposite sound back into your ears, which cancels out the background noises. Physicist Werner Meyer-Eppler had been influenced by Homer Dudley's 1948 invention of the Vocoder and started in 1951 to work https://www.youtube.com/watch?v=M1nIb_K2rEo