Implementation of multiple voices in an electronic musical instrument

摘要

A polyphonic tone synthesizer in which two or more distinct voices are sounded by operation of a single key. While the voices have the same fundamental frequency, they are made audibly distinct by differing in harmonic content and differing in the shape of the envelope of the voice signal. The two or more voices are synthesized by alternately calculating master data lists of the amplitude values representative of points on the waveforms of the two voices, adding the two master data lists and converting the resulting values to an analog waveform by feeding the data to a digital-to-analog converter at a rate determined by the fundamental frequency of the note. The master data list for each voice is calculated repetitively during the time the key is operated by multiplying a set of coefficients with a set of sinusoid values and continuously scaling the resultant product by an envelope scale factor which changes with time to correspond to the desired envelope waveform. A single ADSR (attack/decay) generator may be time shared with each voice calculation to provide a differently changing envelope scale factor for each voice.