Active Noise Cancellation tunes out distracting and annoying background noise. It is turned on by default after you've created your personal audio profile for the first time.
With the HTC USonic earphones plugged in, hear music, videos, or games clearly without needing to turn up the volume in loud environments. When you don't need Active Noise Cancellation, you can turn it off.
Important: In some regions, you may need to download and install the latest system update to turn Active Noise Cancellation on or off separately from your personal audio profile.