When the NC is on, it makes a slight squeal on the side where the electronics are. While music is playing, this is not heard, but if there is no music playing, it can be heard for a few seconds, and then a noise gate silences the noise. His voice is good for the money. Somewhere it was written that if NC is turned on, the bass will be reduced. In fact, the sound image is more balanced when the NC is switched on, probably not only does it filter noise, but the DSP also improves something on the frequency response. The NC can also be turned on without music, so it can be used purely for noise filtering.