Musical tone-generating method and apparatus capable of approximating envelope characteristic of a waveform of a musical tone by a polygonal line

摘要

A musical tone waveform sample is generated at each sampling time by the use of a processing unit carrying out an arithmetic operation every repetition period that is longer than the sampling time. An envelope characteristic of a waveform of a musical tone to be generated is approximated by a polygonal line formed by a plurality of segments each of which has a length corresponding to the repetition period. An envelope value of a first waveform sample of waveform data of the musical tone to be generated for the repetition period is determined. The envelope value of the first waveform sample is multiplied by a predetermined attenuation factor to obtain an envelope value of a last waveform sample of the waveform data for the repetition period. Each of the segments of the polygonal line is determined by the envelope value of the first waveform sample and the envelope value of the last waveform sample. A difference between the envelope values of the first and last waveform samples is calculated. A decremental or incremental value per the each sampling time is obtained based on the difference. The envelope value of the waveform at the each sampling time is determined by adding the decremental or incremental value to an immediately preceding value of the envelope value of the waveform.