Originally Posted by osxanalyst
This is totally false. The NC headsets only work with repetitive sounds such as engines, etc. Human speech is not canceled out as the frequencies are constantly varying (impossible to cancel). In fact, it is easier to hear conversations with the NC headsets on as it wipes out the background noise, but not human conversation.
Actually, I think it is the frequency of the sound, not the varying of the pitch. I guarantee you that if you had a truly monotone sound (say, like a piano key) at any frequency in the mid to high range that you would still hear it.