For each of a number of musical tones, a rectangular square wave generator is programmed to produce a series of rectangular waves of the same amplitude and period, each wave of which has a predetermined energy content. The energy content of the waves is controlled through digital logic to permit adjustment of the amount and timing of the delivery of the driving force to a sound transducer. By appropriate adjustments in the energy content and utilization of the characteristics of the particular sound transducer, musical tones having substantially the same aural characteristics as those of a number of musical instruments can be produced.