A hardware multitone digital frequency synthesizer

The synthesis of two or more tones simultaneously has numerous applications, including telephone signaling, music synthesis, waveform generation, and man-machine communications. We describe a hardware approach in which the basic tones are generated digitally for accuracy and stability, using time-shared circuitry. The tones are combined and their levels are controlled by an analog approach using a pair of D/A converters, avoiding digital multipliers and adders. Performance and description of a hardware prototype are given.