Digital tone synthesizer and beat indicator for tuning musical instruments
M. Ward Widener · The Journal of the Acoustical Society of America · 1975
Using a stable quartz oscillator and low-powered digital logic, a musical tone synthesizer has been developed to produce scales with any tempering of intervals based on any selected tuning reference pitch. A clock frequency of 3.5 MHz permits A-440 to be set closer than 0.11 Hz, or 0.43 cents. The logic includes a 12-bit presettable binary counter which is programmed to divide by a selected number of clock pulses. The binary number is encoded in a standard computer card and interpreted by a special mechanical card reader. The first octave can be divided into 1988 intervals. In addition to the equally tempered scale, cards have been encoded for Pythagorean, mean tone, and just intonations in a wide variety of reference pitches. The direction and magnitude of tuning errors are shown on a solid-state display driven by a type of ring counter. The result is a compact portable instrument that is both accurate and programmable to the pitch requirements of the user.