US 3,972,259 A · Production of pulse width modulation tonal effects in a computor organ

Abstract

In a computor organ, musical tones are generated by separately evaluating the constituent Fourier components of a musical waveshape and summing these to obtain the waveshape sample point amplitudes. The relative amplitude contribution of each Fourier component is established by a harmonic coefficient. In accordance with the present invention, pulse-type tone generation is simulated by using harmonic coefficient values associated with the frequency spectrum of a pulse train of particular pulse shape. For example, the coefficients may be given by the Fourier transform associated with repetitive pulses. To simulate pulse width modulation effects, a set of such coefficients is stored in a memory, the set having more coefficients than the maximum number of Fourier components included in each amplitude computation. Pulse trains of different pulse width are simulated by utilizing different subsets of the stored coefficients in the amplitude computation. Pulse width modulation tonal effects are achieved by changing the selected subsets as a function of time.

Claims11

Dependent claims

In an electronic musical instrument of the type including generation means wherein musical tones are generated by computing in real time the amplitudes at successive sample points of that waveshape, said waveshape amplitudes being converted to musical tones as the computations are carried out, said generation means including calculation circuitry for separately calculating the constituent Fourier components of a musical waveshape, and an accumulator for summing these components to obtain each waveshape sample point amplitude, and wherein the relative amplitude of each constituent Fourier component with respect to each other is established by a harmonic coefficient associated with the order of that component, the improvement for simulating the tonal quality of a repetitive pulse train having a particular pulse shape comprising;

coefficient supply means for providing a set of harmonic coefficient values that define the frequency spectrum of said pulse train of particular pulse shape, and
control means, connected to said coefficient supply means and to said generation means, for causing said supply means to provide a certain subset of said coefficient values to said calculation circuitry to establish said Fourier component relative amplitudes.

In an electronic musical instrument of the type including generation means wherein musical tones are generated by computing in real time the amplitudes at successive sample points of that waveshape, said waveshape amplitudes being converted to musical tones as the computations are carried out, said generation means including calculation circuitry for separately calculating the constituent Fourier components of a musical waveshape, and an accumulator for summing these components to obtain each waveshape sample point amplitude, and wherein the relative amplitude of each constituent Fourier component is established by a harmonic coefficient associated with the order n of that component, the improvement for simulating pulse width modulation tonal effects, comprising;

a memory storing a set of harmonic coefficients C.sub.m that define the relative amplitudes of the components in the frequency spectrum of a pulse train of particular pulse shape, where m designates the order in that spectrum, said set including a number of coefficients C.sub.m for components of order greater than the highest order n.sub.max Fourier component included by said accumulator in each waveshape amplitude summation,
subset selection circuitry for providing a time varying factor p that establishes the subset of harmonic coefficients C.sub.m to be utilized by said calculation circuitry,
order designating means, connected to said calculation circuitry, for providing a signal n that indicates the order n of the Fourier component currently being calculated by said calculation circuitry,
an adder for summing the factor p from said selection circuitry and the signal n from said designating means to obtain the value m=p+n, and
a memory access control for accessing from said memory the harmonic coefficient C.sub.m corresponding to the value m=p+n obtained by said adder, said instrument utilizing this accessed coefficient C.sub.m =C.sub.(p.sub.+n) to establish the relative amplitude of the n.sup.th order Fourier component currently being calculated.

2 more elements

Dependencies are inferred from the claim text.

Production of pulse width modulation tonal effects in a computor organ

Life of this patent

Production of pulse width modulation tonal effects in a computor organ

Life of this patent

Abstract

Claims11