XPost: sci.electronics.design   
   From: joseph_barrett@sbcglobal.net   
      
   On Fri, 20 Jan 2012 13:10:59 -0500, Dick Pierce    
   wrote:   
      
   >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.   
      
   Where does the energy for all that processing and mixing come from?   
      
   ?-)   
      
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