Apparatus for reducing noise in digital to analog conversion

Claim 2

In a musical instrument having a waveshape memory storing a plurality of data points corresponding to the amplitudes of a corresponding number of evenly spaced points defining a cycle of an audio musical signal and in which said data points are sequentially and repetitively read out of the waveshape memory and transferred to a digital-to-analog converter at a rate proportional to the pitch of the musical tone being generated, apparatus for reducing undesired frequency components in the musical tone comprising; a waveshape memory storing said plurality of waveshape data points, note clock means for generating timing signals at a rate proportional to the pitch of the musical tone, assignor means responsive to said timing signals whereby a predetermined number M of said data points are addressed out in a consecutive order from said waveshape memory and wherein the memory address of the first said addressed data point is advanced modulo the number of data points in said plurality of waveshape data points in response to said timing signal, a plurality of memories each storing identical sets of smoothing function data values wherein said plurality of memories is equal to said predetermined number M, addressing means responsive to said timing signals for addressing smoothing function data values from said plurality of memories, a multiplicity of multiplication means wherein said waveshape data points addressed out from said waveshape memories are multiplied by said smoothing function data values addressed out from said plurality of memories, a summing means for adding all the product values from the totality of said multiplicity of multiplication means to create an output set of waveshape data points thereby reducing said undesired frequency components, and a signal conversion means wherein said output set of waveshape data points is converted to an analog waveform.

Claim 3

A musical instrument according to claim 1 wherein said plurality of memories stores smoothing function data values computed according to the relation x.sub.n =sin (πn/M)/(πn/M) where n is the index for each address in a member of said plurality of memories and M is the number of memories in the plurality of memories.

Claim 4

A musical instrument according to claim 1 wherein said plurality of memories store smoothing function data values computed from values of the Bessel function J 0 (A) for increments of A equal to 2.4083/M where M is the number of memories in the plurality of memories.

Claim 5

A musical instrument according to claim 1 wherein the plurality of data words defining a cycle of the audio signal is a set of N values and wherein said plurality of memories comprises; a multiplicity of M memory means each corresponding to one of said plurality of memories and each containing identical sets of N smoothing function data values wherein each said smoothing function data value is stored at a memory address (n+jh) where j is an index designating a member of said plurality of memories, n is an index in the range 1,2, . . . , N, h is a phase offset number value, and (n+jh) is a number modulo N.

Claim 6

A musical instrument according to claim 1 wherein the plurality of data words defining a cycle of the audio signal is a set of N values and wherein said addressing means further comprises; phase addressing means whereby smoothing function data addressed out from a plurality of M memories each storing identical sets of said smoothing function data are addressed out in a sequence of values according to the memory address index number (n+jh) and j is an index designating a member of the plurality of memories, n is the sequence index number, h is a phase offset number value, and (n+jh) is a number modulo N.

Claim 7

A musical instrument according to claim 1 wherein the plurality of data words defining a cycle of the audio signal is a set of N values and wherein said assignor means further comprises; assignment circuitry for transferring the M data words addressed out from said waveshape memory in a cyclic order to members of said plurality of multipliers.

Claim 8

In a musical instrument having a waveshape memory storing a plurality of data words corresponding to the amplitudes of N evenly spaced points defining a cycle of a musical waveshape and in which said data words are sequentially and repetitively read out of the waveshape memory and transferred to a digital-to-analog converter at a rate proportional to the pitch of the musical tone being generated apparatus for reducing undesired frequency components in the audible musical signal comprising; a smoothing memory for storing smoothing function data values, note clock means for generating timing signals at a rate proportional to the pitch of the musical tone, assignor means responsive to said timing signals whereby a sequence of a predetermined number n of said data points are repetitively addressed out in consecutive order from said waveshape memory and wherein the memory address of the first member of said sequence of addressed data points is advanced modulo the number of data points in said plurality of waveshape data points in response to said timing signals, phase addressing means responsive to said timing signals whereby a sequence of smoothing function data values are addressed out from said smoothing function memory according to an index number (i+jh) which is a number modulo said number N, j is a device number having integer values in the range of 1 to said number n, i is the index number of said sequence of consecutive data points addressed out from said waveshape memory, and the constant h is a phase offset number, a plurality of multiplication means, of said number n and each designated by said device number j wherein each of said data words addressed out by said phase addressing means is multiplied by a corresponding one of said data words addressed out by said assignor means, a summing means for adding all the product values produced by said plurality of multiplication means to create an output set of waveshape points thereby reducing said undesired frequency components, and a signal conversion means wherein the output of said summing means is converted to an analog signal waveform.

Claim 9

In a musical instrument having a waveshape memory storing a plurality of data words corresponding to the amplitudes of N evenly spaced points defining a cycle of a musical waveshape and in which said data words are sequentially and repetitively read out of the waveshape memory and transferred to a digital-to-analog converter at a rate proportional to the pitch of the musical tone being generated apparatus for reducing undesired frequency components in the audible musical signal comprising; a smoothing memory for storing smoothing function data values, note clock means for generating timing signals at a rate proportional to the pitch of the musical tone, assignor means responsive to said timing signals whereby a sequence of a predetermined number n of said data points are repetitively addressed out in consecutive order from said waveshape memory and wherein the memory address of the first member of said sequence of addressed data points is advanced modulo the number of data points in said plurality of waveshape data points in response to said timing signals, phase addressing means responsive to said timing signals whereby a sequence of smoothing function data values are addressed out from said smoothing function memory according to an index number (i+jh) which is a number modulo said number N, j is a device number having integer values in the range of 1 to said number n, i is the index number of said sequence of consecutive data points addressed out from said waveshape memory, and the constant h is a phase offset number, a plurality of multiplication means, of said number n and each designated by said device number j wherein each of said data words addressed out by said phase addressing means is multiplied by a corresponding one of said data words addressed out by said assignor means, a summing means for adding all the product values produced by said plurality of multiplication means to create an output set of waveshape points thereby reducing said undesired frequency components, and a signal conversion means wherein the output of said summing means is converted to an analog signal waveform.

Claim 10

A musical instrument according to claim 7 wherein said smoothing function memory stores smoothing function data computed according to the relation x.sub.n =sin (πn/M)/(πn/M) where n is the index for each address in the smoothing function memory and M is the number of members in said multiplicity of multipliers.

Claim 11

In a musical instrument having a waveshape memory storing a plurality of data words corresponding to the amplitudes of N evenly spaced points defining a cycle of a musical waveshape and in which said data words are sequentially and repetitively read out of the waveshape memory and transferred to a digital-to-analog converter at a rate proportional to the pitch of the musical tone being generated apparatus for reducing undesired frequency components in the audible musical signal comprising; a smoothing memory for storing smoothing function data values, note clock means generating timing signals at a rate proportional to the pitch of the musical tone, a data storage means for storing data words addressed out from said waveshape memory, data storage select means responsive to said note clock means wherein a sequence of j consecutive data words are repetitively addressed out from said waveshape memory according to an index number i and are stored in said data storage means, wherein the memory address of the first addressed data word in said sequence is advanced in response to said note clock means, phase addressing means responsive to said note clock means whereby a sequence of smoothing function data are addressed out from said smoothing function memory according to an index number (i+jh) which is a number modulo said number N, the constant n is a phase offset number and whereby said addressed smoothing function data are provided as output data, a multiplier means for forming the multiplied values of said output data data from said phase addressing means with the corresponding data words stored in said data storage means, a summing means for adding the multiplied product values provided by said multiplier means to create an output set of waveshape data points thereby reducing said undesired frequency components, and a signal conversion means wherein the output of said summing means is converted to an analog signal waveform.

Claim 12

In a musical instrument having a waveshape memory storing a plurality of data words corresponding to the amplitudes of N evenly spaced points defining a cycle of a musical waveshape and in which said data words are sequentially and repetitively read out of the waveshape memory and transferred to a digital-to-analog converter at a rate proportional to the pitch of the musical tone being generated apparatus for reducing undesired frequency components in the audible musical signal comprising; a smoothing memory for storing smoothing function data values, note clock means generating timing signals at a rate proportional to the pitch of the musical tone, a data storage means for storing data words addressed out from said waveshape memory, data storage select means responsive to said note clock means wherein a sequence of j consecutive data words are repetitively addressed out from said waveshape memory according to an index number i and are stored in said data storage means, wherein the memory address of the first addressed data word in said sequence is advanced in response to said note clock means, phase addressing means responsive to said note clock means whereby a sequence of smoothing function data are addressed out from said smoothing function memory according to an index number (i+jh) which is a number modulo said number N, the constant n is a phase offset number and whereby said addressed smoothing function data are provided as output data, a multiplier means for forming the multiplied values of said output data data from said phase addressing means with the corresponding data words stored in said data storage means, a summing means for adding the multiplied product values provided by said multiplier means to create an output set of waveshape data points thereby reducing said undesired frequency components, and a signal conversion means wherein the output of said summing means is converted to an analog signal waveform.

Claim 13

A musical instrument according to claim 9 wherein said data storage select means further comprises; modulo addressing circuitry whereby said consecutive data words are accessed from said waveshape memory at addresses modulo said number N of points defining a cycle of a musical waveshape, data replacement circuitry responsive to said note clock means whereby data addressed out from said waveshape memory are stored in a cyclic sequence of memory addresses in said data storage means, and data addressing means responsive to said note clock means whereby data stored in said data storage select means are cyclically addressed out and transferred to said multiplier means.

Claim 14

A musical instrument according to claim 9 when said summing means further comprises; an adder-accumulator means for adding and accumulating the sum of said number j of products provided by said multiplier means and transferring the sum to said signal conversion means and wherein the contents of the adder-accumulator are initialized after each said transfer in response to said note clock means.

Claim 15

In a musical instrument having a waveshape memory storing a plurality of data words corresponding to the amplitudes N evenly spaced points defining a cycle of a musical waveshape and in which said data words are sequentially and repetitively read out of the waveshape memory at a rate proportional to the pitch of the musical tone being generated apparatus for reducing undesired frequency components in the audible musical signal comprising; a smoothing function memory for storing smoothing function data values, a multiplicity of first signal conversion means for converting digital data values to analog output signals, data assignor means whereby data words addressed out from said waveshape memory are assigned in cyclic order to members of said multiplicity of first signal conversion means, a multiplicity of second signal conversion means, each member of which corresponds to a member of said multiplicity of first signal conversion means, for generating second output analog signals having magnitudes corresponding to the product of said analog output signals and said smoothing function data values, phase addressing means whereby smoothing function data values stored in said smoothing function memoty are addressed out and transferred to members of said multiplicity of second signal conversion means, and a summing means for adding said second output analog signals from said multiplicity of second signal conversion means thereby reducing said undesired frequency components.

Claim 16

In a musical instrument having a waveshape memory storing a plurality of data words corresponding to the amplitudes N evenly spaced points defining a cycle of a musical waveshape and in which said data words are sequentially and repetitively read out of the waveshape memory at a rate proportional to the pitch of the musical tone being generated apparatus for reducing undesired frequency components in the audible musical signal comprising; a smoothing function memory for storing smoothing function data values, a multiplicity of first signal conversion means for converting digital data values to analog output signals, data assignor means whereby data words addressed out from said waveshape memory are assigned in cyclic order to members of said multiplicity of first signal conversion means, a multiplicity of second signal conversion means, each member of which corresponds to a member of said multiplicity of first signal conversion means, for generating second output analog signals having magnitudes corresponding to the product of said analog output signals and said smoothing function data values, phase addressing means whereby smoothing function data values stored in said smoothing function memoty are addressed out and transferred to members of said multiplicity of second signal conversion means, and a summing means for adding said second output analog signals from said multiplicity of second signal conversion means thereby reducing said undesired frequency components.

Claim 17

A musical instrument according to claim 12 wherein said phase addressing means further comprises phase circuitry whereby smoothing function data are addressed out from said smoothing function memory in a sequence of values according to the index number (n+jh) which is a number modulo said number N, n is the sequence index number, h is a phase offset number, and j is a number equal to the multiplicity of said first conversion means.

Claim 18

A musical instrument according to claim 12 wherein said multiplicity of second signal conversion means further comprises; a multiplicity of amplifier circuits for amplifying said analog output signals from said first signal conversion means and wherein each amplifier circuit is responsive to an analog control signal, a smoothing signal conversion means whereby data values addressed out from said smoothing function memory are converted into analog control signals and transferred to said multiplicity of amplifier circuits.

Claim 19

In a musical instrument having a waveshape memory storing a plurality of data words corresponding to the amplitudes of N evenly spaced points defining a cycle of a musical waveshape and in which said data words are sequentially and repetitively read out of the waveshape memory at a rate proportional to the pitch of the musical tone being generated apparatus for reducing undesired frequency components in the audible musical signal comprising; a note clock timing means wherein timing clock signals are generated, waveshape memory addressing means responsive to said timing clock signals for addressing data words out of said waveshape memory, a signal conversion means whereby data points addressed out of said waveshape memory are converted into analog signals, memory means storing smoothing function values, analog signal storage means wherein said analog signals are stored, data weighting means wherein analog signals stored in said analog storage means are multiplied by smoothing data values from said memory means to provide smoothed analog signals, and summing means wherein all said smoothed analog signals are added together thereby reducing undesired frequency components in the summed musical signal.

Claim 20

In a musical instrument having a waveshape memory storing a plurality of data words corresponding to the amplitudes of N evenly spaced points defining a cycle of a musical waveshape and in which said data words are sequentially and repetitively read out of the waveshape memory at a rate proportional to the pitch of the musical tone being generated apparatus for reducing undesired frequency components in the audible musical signal comprising; a note clock timing means wherein timing clock signals are generated, waveshape memory addressing means responsive to said timing clock signals for addressing data words out of said waveshape memory, a signal conversion means whereby data points addressed out of said waveshape memory are converted into analog signals, memory means storing smoothing function values, analog signal storage means wherein said analog signals are stored, data weighting means wherein analog signals stored in said analog storage means are multiplied by smoothing data values from said memory means to provide smoothed analog signals, and summing means wherein all said smoothed analog signals are added together thereby reducing undesired frequency components in the summed musical signal.

Claim 21

A musical instrument according to claim 15 wherein said analog signal storage means comprises a charge coupled device responsive to said timing clock signals.

Claim 22

A musical instrument according to claim 16 wherein said data weighting means comprises a multiplicity of electrical resistors each connected to an output of said charge coupled device.