Harmonic modulation and loudness scaling in a computer organ

Claim 2

In an electronic musical instrument wherein each note is synthesized in real time, said instrument including calculation circuitry for separately evaluating the constituent Fourier components of each note, and accumulation circuitry for summing said evaluated components, and attack/decay control circuitry for varying the envelope amplitude of each note during attack and decay portions of note synthesis, the improvement wherein said instrument includes harmonic modulation means, connected to said calculation and accumulation circuitry, for preventing certain constituent Fourier components from being included in said summation, in proportion to the note envelope amplitude concurrently established by said attack/decay control circuitry.

Claim 3

An electronic musical instrument according to claim 1, wherein said attack/decay control circuitry includes: an attack/decay scale factor supply circuit for providing a time varying scale factor that establishes the envelope amplitude of the note synthesized by said instrument, and wherein said harmonic modulation means comprises; a divider for dividing said scale factor by a constant to provide a number proportional to said envelope amplitude, and Fourier component inhibit circuitry receiving said number and connected to said calculation and accumulation circuitry to inhibit the inclusion in said summation of all constituent Fourier components having an order higher than said number.

Claim 4

In an electronic musical instrument of the type wherein a musical waveshape is synthesized by computing in real time the amplitudes at successive sample points of that waveshape, said waveshape amplitudes being converted to musical signals as the computations are carried out, said instrument having generation means for individually calculating the constituent Fourier components of that musical waveshape and summing these Fourier components, said generation means including a circuit that establishes the relative amplitudes of said Fourier components in accordance with a set of stored harmonic coefficients that are scaled by a time varying scale factor which establishes the envelope amplitude of said musical waveshape, the improvement for modulating the harmonic content of said musical waveshape in response to the amplitude of said envelope, comprising: first means, responsive to said scale factor, for providing a harmonic-content-designating number which is proportional to the amplitude of said envelope at the time said sample point amplitude computation is carried out, and inhibit means, connected to said generation means and responsive to said first means, for excluding from said sample point amplitude computation certain Fourier components designated by said harmonic-content-designating number.

Claim 5

In an electronic musical instrument of the type wherein a musical waveshape is synthesized by computing in real time the amplitudes at successive sample points of that waveshape, said waveshape amplitudes being converted to musical signals as the computations are carried out, said instrument having generation means for individually calculating the constituent Fourier components of that musical waveshape and summing these Fourier components, said generation means including a circuit that establishes the relative amplitudes of said Fourier components in accordance with a set of stored harmonic coefficients that are scaled by a time varying scale factor which establishes the envelope amplitude of said musical waveshape, the improvement for modulating the harmonic content of said musical waveshape in response to the amplitude of said envelope, comprising: first means, responsive to said scale factor, for providing a harmonic-content-designating number which is proportional to the amplitude of said envelope at the time said sample point amplitude computation is carried out, and inhibit means, connected to said generation means and responsive to said first means, for excluding from said sample point amplitude computation certain Fourier components designated by said harmonic-content-designating number.

Claim 6

An electronic musical instrument according to claim 3 wherein said first means comprises; a divider circuit for dividing said scale factor by a constant and for rounding off the quotient to obtain said harmonic-content-designating number, and wherein said inhibit means excludes from said sample point amplitude computation those Fourier components having an order higher than that designated by the rounded off quotient obtained by said divider circuit.

Claim 7

An electronic musical instrument according to claim 4 wherein S(t)max is the maximum amplitude of said envelope, wherein W is the highest order Fourier component that can be included in said sample point amplitude computation, and wherein said constant is the next higher integer nearest the value S(t)max/W.

Claim 8

An electronic musical instrument according to claim 3 wherein said first means comprises; a memory storing a set of harmonic-content-designating numbers each associated with a different range of envelope amplitude scale factor values, and control means for ascertaining which range contains the scale factor currently being utilized by said circuit and for accessing from said memory the harmonic-content-designating number associated with that range.

Claim 9

An electronic musical instrument according to claim 3 wherein said generation means comprises; at least one attack, sustain or decay scale factor memory from which successive scale factor values are accessed during respective attack, sustain and decay portions of musical waveshape production, said values being supplied to said first means, said first means Providing said harmonic-content-designating number in response to the scale factor value currently being supplied.

Claim 10

An electronic musical instrument of the type having tone generation means for computing in real time the successive sample point amplitudes of a musical waveshape, said generation means including evaluation circuitry for separately evaluating the constituent Fourier components, an accumulator for summing these components to obtain each sample point amplitude, and a converter for converting the obtained amplitudes to musical tones, the fundamental frequency of the generated tone being established by a frequency number utilized by said evaluation circuitry in each Fourier component evaluation, the improvement wherein the loudness of the tones at lower frequencies is augmented to compensate for the decreased response of the human ear at such frequencies, comprising; loudness scaling circuitry, receiving said frequency number from said generation means, for providing a loudness scale factor having different values for different ranges of tone fundamental frequency as established by said frequency number, and multiplier means, receiving said loudness scale factor from said circuity and cooperating with said generation means, for multiplying said obtained amplitude by said loudness scale factor, the resultant increase in loudness of the generated musical tone compensating for said decreased aural response.

Claim 11

An electronic musical instrument of the type having tone generation means for computing in real time the successive sample point amplitudes of a musical waveshape, said generation means including evaluation circuitry for separately evaluating the constituent Fourier components, an accumulator for summing these components to obtain each sample point amplitude, and a converter for converting the obtained amplitudes to musical tones, the fundamental frequency of the generated tone being established by a frequency number utilized by said evaluation circuitry in each Fourier component evaluation, the improvement wherein the loudness of the tones at lower frequencies is augmented to compensate for the decreased response of the human ear at such frequencies, comprising; loudness scaling circuitry, receiving said frequency number from said generation means, for providing a loudness scale factor having different values for different ranges of tone fundamental frequency as established by said frequency number, and multiplier means, receiving said loudness scale factor from said circuity and cooperating with said generation means, for multiplying said obtained amplitude by said loudness scale factor, the resultant increase in loudness of the generated musical tone compensating for said decreased aural response.

Claim 12

An electronic musical instrument according to claim 8 wherein said tone generation means includes; note selection switches, and a frequency number memory containing frequency number values associated with notes of the musical scale, selection of one of said note switches causing the associated frequency number to be supplied from said memory to said generation means and to said loudness scaling circuitry, and wherein said loudness scaling circuitry comprises; a scale factor memory containing a set of loudness scale factors associated with different octaves or fractions of an octave, and a memory access control, responsive to the supplied frequency number, for accessing from said scale factor memory the loudness scale factor associated with the octave or fractional octave containing the note having a fundamental frequency specified by said frequency number.

Claim 13

An electronic musical instrument according to claim 9 wherein said frequency number memory also contains a code associated with each frequency number, said code specifying the octave or fractional octave of that frequency number, said memory access control being responsive to said code.

Claim 14

An electronic musical instrument according to claim 8 wherein said Fourier components are summed in an accumulator, and wherein said multiplier means comprises a circuit for multiplying each total sum obtained in said accumulator by said loudness scale factor prior to conversion of said sums to musical tones.

Claim 15

An electronic musical instrument according to claim 8 wherein the amplitude of each constituent Fourier component is established by a corresponding harmonic coefficient, and wherein said multiplier means comprises a scaler circuit for multiplying each of said harmonic coefficients by said loudness scale factor.

Claim 16

An electronic musical instrument for producing musical tones having a harmonic content that is modulated in response to the amplitude of the produced tone during attack, sustain and decay, comprising: first means for computing at regular time intervals tx the amplitudes Xo(qR) of a waveshape, where q is an integer incremented each time interval tx, in accordance with the relationship

Claim 17

An electronic musical instrument for producing musical tones having a harmonic content that is modulated in response to the amplitude of the produced tone during attack, sustain and decay, comprising: first means for computing at regular time intervals tx the amplitudes Xo(qR) of a waveshape, where q is an integer incremented each time interval tx, in accordance with the relationship

Claim 18

An electronic musical instrument according to claim 13 wherein said harmonic inhibit circuitry comprises; a divider for dividing the scale factor S(t) currently being provided by said attack/decay scale factor circuitry by a constant k, the value nmax being equal to the quotient rounded-off to an integer, and a comparator for comparing said value nmax supplied from said divider with the order n for which said first circuitry is currently providing values, and for providing an inhibit signal to said harmonic coefficient supply circuitry when n>nmax, said inhibit signal causing the supplied coefficient Cn to equal zero.

Claim 19

An electronic musical instrument according to claim 13 wherein said first means further comprises; a frequency number memory storing a set of values R for selectable notes, note selection switch circuitry for accessing from said frequency number memory a value R associated with a selected switch, and a note interval adder of modulo 2W incremented by the accessed value R at each time interval tx to obtain the value qR, and wherein said attack/decay scale factor circuitry comprises; an attack and decay scale factor memories storing sets of scale factors S(t), and attack/decay control logic for successively accessing said scale factors from the attack and decay scale factor memories at a rate coincident with generation of successive fractional cycles of the produced tone, as established by the contents of said note interval adder.

Claim 20

An electronic musical instrument according to claim 13 wherein the loudness of the produced musical tone is scaled to compensate for reduced aural sensitivity of the listener at low frequencies, comprising; loudness scaling logic, responsive to the frequency number R of the selected note, for providing a loudness scale factor L(R) inversely related to said aural sensitivity at the frequency of said selected note, and a scaler for scaling each generated sample point amplitude Xo(qR) by the provided loudness scale factor L(R).