A microphone whose directional characteristics are the result of acoustic phase shifts within the microphone. A uni-directional microphone.
"I just want to tell you how pleased I am about the work you did for me recently. You took an old 3 inch reel with the voice of my mother-in-law who has been deceased thirty-three years and converted it to a CD. That old tape was found in our basement, stored there for twenty years. I asked you to convert it in time for Christmas, which you did. ..."