This invention relates to a method of synthesizing musical tones.
A musical tone or natural tone produced by an acoustic or natural musical instrument can be expressed by a Fourier series expansion as shown below ##EQU1## where a.sub.n (t) denotes an envelope function of an n-th harmonic component varying with time, .phi.n the phase of the n-th harmonic component, .omega. the angular frequency of a fundamental tone, and N the number of partial frequency components included in the musical tone.
As will be evident from equation (1), the amplitudes of spectral components composing a musical tone vary independently with time. That is, a natural tone or actual musical instrument tone is characterized by a dynamic audio spectrum.
The simulation of a natural tone with the dynamic audio spectrum can be electronically realized by the use of N envelope function generation circuits, N multipliers and N sinusoidal signal generation circuits. However, since the value of N is relatively large, the actual realization is very difficult.
In an existing music synthesizer, a cut-off frequency or frequencies of a voltage-controlled filter is controlled or modulated by a control waveform having a desired shape. The cut-off frequency control of the voltage-controlled filter, however, only vary a frequency range over which higher harmonic components are distributed, and the frequency spectrum of a musical tone being produced substantially remains unchanged. With the music synthesizer it is considerably difficult to obtain dynamic audio spectra.