In order to manipulate and store sounds, we need a representation that can be easily transferred from point to point, altered to suit our wishes, and stored in a permanent fashion. A simple and flexible such representation is the flow of electrons, or electricity. We use an electromechanical device, a microphone, to convert the air pressure variations of sound into an analogous flow of electrons. It is then simple to distribute the electrons through a wire to other places. It is also possible to convert the flow of electrons into magnetic flux that can be stored for ...