According to experience of mine and of my friends using active noise cancellation headphones, the technology is much more efficient in reducing "periodic" noise, such as humming of jet engine, fridge etc., than reducing "non-periodic irregular" noise, such as human voice.
Is it only a personal perception, or is it a measurable fact with some deeper reason behind it?
I cannot imagine why it should work like this. Intuitively, the speakers must produce the "anti-noise" not regarding the periodicity of the noise.
I understand the difference between characteristics of a periodic sound and the human voice. However I still don't get how it applies to the anti-noise headphones. They cannot simply play the anti-wave against the last remembered wave, they have to play the anti-wave against the new wave. So how does it help if the headphones know what the last wave was?