ANC doesn't ever provide perfect isolation. If you see advertisements ANC it will say "blocks 99% of sound" or "cancels 99.9% of noise" which is equivalent to a

ANC doesn't ever provide perfect isolation. If you see advertisements ANC it will say "blocks 99% of sound" or "cancels 99.9% of noise" which is equivalent to a 20dB and 30dB drop respectively. You're right though that it doesn't work as well at high volumes. The louder the noise, the more distortion in the microphone/amplifier/driver, so the efficacy of the noise cancelling is reduced. For example in this THD graph of the AirPod Pro's, at 100dB it adds approximately 3dB compare to the 90dBtest.[1] Going much louder and you'll start getting digital clippings as the built in amplifier won't have enough range. > . For example, if a car beeped its horn at you while using ANC, i hear it. Car horns are above 100dB, and at the frequency they are, APD only measures about 20dB of attenuation [2], so that only brings it down to 80dB, which is still very loud. > ANC is merely for constant low background noise like airplane engine. What I find very neat is that even though only 20-30dB of isolation is measured, many noises really do "go away". If you play around with ANC you'll realize that as the background noise gets louder, the white noise hiss from the ear piece gets louder. This mostly the result of error in the system, but this increase in background noise has the effect of masking any external sounds that make it through. I believe it also moves a lot of that energy to higher frequencies where you don't notice it. [1] https://www.rtings.com/headphones/1-4/graph#1625/4029 https://www.rtings.com/headphones/1-4/graph#1625/4029 [2] https://www.rtings.com/headphones/1-4/graph#1625/4053 https://www.rtings.com/headphones/1-4/graph#1625/4053