8d0c15fd   
   XPost: sci.electronics.design   
   From: dpierce@cartchunk.org   
      
   On 1/19/2012 11:20 PM, RichD wrote:   
   > A noise canceling headphone consists of a headphone,   
   > plus an external microphone fed to an inverting input,   
   > right?   
      
   Well,  not quite.   
      
   It also includes some signal processing, mixing   
   capability to properly blend the processed mic   
   signal with the incoming music signal, amplifiers   
   to power the headphone drivers themselves, the   
   mechanical packaging to hold it all together, etc.   
      
   > Why does that cost $40 extra?   
      
   It costs extra because of the signal processing,   
   mixing capability to properly blend the processed   
   mic signal with the incoming music signal, amplifiers   
   to power the headphone drivers themselves, the   
   mechanical packaging to hold it all together, etc.   
      
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