Active noise cancelation
To provide active noise cancelation, internal and external microphones measure unwanted ambient noises, then circuity in the headphones generates sound at a frequency that cancels out those noises. Active noise cancelation works whenever headphones with this feature are turned on.
Adaptive noise cancelation is a type of heightened noise cancelation. When you're listening to music, speaker output strikes a balance between audio quality and noise cancelation. When you're not listening to music, the level of noise cancelation automatically increases to block outside sounds.