What added audio? ANC doesn't add anything.I understand you read how ANC works and got scared of it. I can assure you that there is nothing unnatural or unusual in this process. Sounds cancel other sounds all the time. When you speak, your voice bounces off other things and people and gets partially cancelled. When a guitar plays, it cancells some of it's own frequencies, which is why it has it's characteristic timbre. Cancellation means being quieter just like absorption or isolation. If you have a positive pressure and a negative pressure in the same space, they cancel out and you're left with no change in pressure. Just peaceful silence with no side effects.

Think of it this way - if it's getting colder, but you turn on heating, you have constant temperature. It's exactly the same with ANC, except the change is happening very fast. Since 'you turn the heater on and off' just as fast, the temperature is constant and your room cosy. Sound works in the same way, just instead of heat, there are tiny changes in pressure. ANC keeps the pressure constant and on the same level as outside the headphones. To your ears it's very relaxing.