The DUET NC noise cancellation button is located on the bottom Right ear cup. To turn the Active Noise Cancellation on, press and hold the button (Located next to the Bluetooth button) for 2-3 seconds or until you hear the confirmation audio tone. To turn off the noise cancellation, press and hold for 2 seconds or until you hear the audio tone powering off. A white LED next to the button lights up when NC is on.