You can get an explanation of how this noise canceling technology
works if you go to the products section of the Bose web site and
look at the headset for aviation.  See http://www.bose.com/

Jack Breen
Southboro, MA

 [ The standard technique identifies the stationary waveforms
 [ (up to about 500 Hz) and cancels them, leaving just the
 [ random sounds like speech to be heard.  It works remarkably
 [ well against the drone in the cabin of a propellor aircraft.
 [  -- Robbie