My noise cancellation headphone arrived today. The principle of noise cancellation is using a DSP processor, generate pink noise and out of phase sounds to cancell the incoming sound wave sample by the microphone on both side. This type of headphone used to cost over $100, some high end model made by Bose even cost over $300. My headphone is made by Creative Labs, only cost me $30 ordering on eBay. According to PC Magazine, it has 90% performance of the Bose headphone. Probably the advance and cost reduce of DSP make cheap noise cancellation headphone possibly. The sound quality is pretty good, it filters out the annoying air conditionor noise at work. The only complain is the headphone is a bit hot, since it has to cover the whole ear.