Tone generation system employing triangular waves

Abstract

A digital technique for triangular musical waveform generation is disclosed. A musical scale value corresponding to a selected note is repetitively added to produce an ascending series of non-consecutive numbers which is stored in a latch. A carry output from the limited modulus latch is used to switch a flip-flop which then enables an inverter to reverse the slope of the number series. Alternating reversals produce a rising and falling numerical staircase of controllable slope. This can be directly converted into a smooth triangular waveform, or alternatively it can be used as a series of memory addresses for table look-up purposes. The triangular waveform may be symmetrical, or it may have a controlled degree of asymmetry. Duplicate triangular waveforms with a small frequency mismatch may be used to produce a chorus effect. Or plural triangular waveforms with octavely related frequencies may be used as footages related to a single note, again with a slight frequency mismatch for chorus purposes. The frequency mismatch is effected by introducing extra pulses into the ascending number series by means of a synchronized carry input to the latch. When used in the table look-up mode, the invention permits great savings of waveshape memory capacity by the use of half-cycle and quarter-cycle symmetry. The latter feature is achieved by the use of a format translation from binary offset to sign-magnitude notation for table look-up purposes, after which the resulting waveshape is converted back into the original binary offset notation. The table look-up approach is also used in conjunction with plural triangular waveforms, by virtue of time-division multiplexing.