. . . "BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of a guitar, which is the preferred embodiment of this invention; FIG. 2 is a block diagram of circuitry used in this preferred embodiment; FIGS. 3A and 3B are a block diagram and a group of timing diagrams respectively, showing the preferred arrangement and operation of a control signal developing part of the multiplexing circuitry used in th" .