The AKG K490 NC (noise cancelling) headphones offer great sound, great style,  and noise cancelling at an affordable price. To my ears the sound does not change when NC is turned on/off. The background noise just fades away. If you are listening to an audio source when you turn noise cancelling on, the source is muted until noise cancelling is up and running - about one second or so. Then the difference in sound is like stepping into a quiet lounge from a busy street, and being able to hear every nuance in the music without the outside rumble.    I...