Anharmonic overtone generation in a computor organ

摘要

The production of musical notes containing anharmonic overtones is implemented in a computor organ of the type disclosed in U.S. patent application Ser. No. 225,883, filed Feb. 14, 1972, and now U.S. Pat. 3,809,786. In such an instrument, the sampled amplitudes of a musical waveshape are computed in real time by individually calculating the amplitude contributions of the Fourier components constituting the waveshape. In accordance with the present invention, certain of these Fourier components are evaluated at frequencies offset from multiples of the nominal fundamental frequency of the note being generated. This is accomplished by utilizing in the overtone amplitude calculations offset values eta nu which establish the extent of anharmonicity of each overtone. This results in complete freedom of control of the anharmonicity of individual overtones. The overtone offset ( eta nu ) values may be stored in a memory, or may be generated by appropriate circuitry. In certain embodiments the offset is proportional to the frequency of the note being produced, preferably being a constant number of cents. Other embodiments include, among other things, constant frequency offset independent of time, time variant anharmonicity, offset of alternate overtones in opposite frequency directions, and overtone selection to insure correct frequency of a subjective fundamental.