Noise-cancelling headphones use analogue and electronic methods to block out the environmental sound around you, allowing you to listen to your music in peace without distraction. Most noise-cancelling headphones make use of the following two approaches:
Passive noise cancellation: this is when the headphones physically block outside sound from reaching your ears, and this can be achieved in a number of ways. Noise-cancelling over-ear headphones typically have heavily padded earcups to achieve this, while in-ear headphones need to fit snugly in your ear to create a tight seal, stopping environmental sounds from entering.
Active noise cancellation: this method uses inbuilt microphones to analyze environmental noise and create 'anti-noise' frequencies that are mixed in with your music playback. This effectively cancels out the sound of your surroundings using analogue or digital filters.