Note frequency generator for a polyphonic tone synthesizer

摘要

A frequency generator for a keyboard operated electronic music instrument using a single master clock source for selectively producing all the notes of the musical scale. A set of frequency numbers corresponding to each of the notes of a diatonic scale are stored in a memory. A frequency number is selected from the stored numbers according to the note to be generated when a key on a keyboard is activated, the selected number being applied to an adder-accumulator periodically at the master clock rate for incrementing the contents of the accumulator. Overflow pulses from the adder-accumulator shift amplitude values sequentially from a set of values stored in a shift register through an adder to a digital-to-analog converter. The adder modifies the amplitude values by applying a fractional part of the incremental difference between each value and the next value in the sequence to the adder. The fractional amount is determined by the content of the adder-accumulator and changes with each master clock pulse.