Abstract: In a musical instrument having one or more tone generators in which a plurality of data words corresponding to the amplitudes of a corresponding number of evenly spaced points defining the waveform of one cycle of an audio signal are transferred sequentially from a note register to a digital-to-analog converter in repetitive cycles at a rate proportional to the pitch of the tone being generated, apparatus is provided for varying the spectral content of the tone in response to control signals. A loudness control signal causes loud tones to be produced with a greater number of harmonics than those for a soft tone. A formant control signal also causes the tones to have a time variant spectral quality.

Abstract: In an electrical tone generator apparatus is provided for automatically selecting one of a library of chord types which is closest to a chord fingered on a fretted string instrument. The closest decision is made by processing the fingered fret input data by a set of matched filters each of which corresponds to a member of the library of chord types. The chord type decision is made to correspond to the matched filter producing the maximum output response. The selection between chord types yielding equal responses is resolved by priority logic based upon the frequency of chord usage. A root note is chosen for each chord type. Note keying data is generated from the selected chord types which is transposed to the correct musical pitches in response to the chosen root note. The note keying data is grated by an automatic rhythm generator and the output is used to actuate electronic musical tone generators.

Abstract: In a musical instrument having one or more tone generators in which a plurality of data words corresponding to amplitudes of a corresponding number of evenly spaced points defining the waveform of an audio signal composed of a number of unified tones are generated by the combination of three master data sets. The three master data sets are computed separately from stored sets of even and odd harmonic coefficient values. The master data set values are combined using their symmetric properties and are transferred sequentially to a digital-to-analog converter in repetitive cycles at a rate proportional to the unison pitch of the corresponding keyboard note to produce the tone color of a combination of unified tones.

Abstract: In an electrical keyboard musical instrument apparatus is provided for automatically selecting one of a library of chord types which is closest to a chord played on the instrument. The closest decision is made by processing the actuated keyswitch data by a set of matched filters each of which corresponds to a member of the library of chord types. The chord type decision is made to correspond to the matched filter producing the maximum output response. The selection between chord types yielding equal responses is resolved by priority logic based upon the frequency of chord usage. A root note is chosen for each selected chord type.

Abstract: A tone synthesizer for generating a musical tone where harmonic content can be varied with time to produce unique sound effects. This is accomplished by generating waveform data in time sequence, delaying the waveform data by a time interval that is variable, and subtracting the delayed data from the waveform data to provide a modified sequence of waveform data which is then converted to an audio wave.

Abstract: In a musical instrument having one or more tone generators in which a plurality of data words are transferred sequentially from note registers in repetitive cycles at rates proportional to the pitches of tones being generated, apparatus is provided for varying the spectral content of tones having both harmonic and nonharmonic overtones. Control signals are used to vary the amplitudes of the overtones. An independent formant control signal causes the tones to have a time variant spectral quality.

Abstract: In an electronic musical instrument apparatus is provided for producing a noise-like signal suitable for a variety of musical effect such as the imitation of percussive musical instruments. A noise master data set is created repetitively and independently of tone generation by computing a Fourier algorithm using random values for the Fourier coefficients. The noise master data set is transferred to a noise tone register whose output is sequentially and repetitively read and converted to an analog noise signal. Formant circuitry is used to vary the noise signal's spectrum in a time variant manner and the frequency of an assigned variable frequency clock can be used to vary the spectral bandwidth of the output noise signal.

Abstract: A complementer for floating point binary numbers utilizes two digital logic decision rules selected by the value of the power of the input number. The first decision rule is selected for an input power of -1 and constructs a power and mantissa determined by the binary sequence form of the input mantissa. The second decision rule is selected for input powers less than -1 and constructs a mantissa determined by the binary sequence form of the input mantissa and the value of the power. The complemented power is set to a -1 value. The complementer is advantageously employed in digital electronic musical instruments.

Abstract: In a digital tone synthesizer of a type using digital data representing the amplitudes of a predetermined fixed number of sample points along one cycle of the audio waveform of a musical tone and an oscillator controlling the sampling frequency as well as the pitch of the tone, a digital filter for transferring the digital data to a digital-to-analog converter at the sampling rate. The digital filter, in response to applied input coefficient values, operates as a low pass or high pass filter in which the cut-off frequency is a predetermined harmonic of the pitch frequency of the tone. By changing the coefficient values, the cut-off harmonic can be changed for a tone independently of the pitch of the tone. Thus any tone of the musical scale may be filtered to modify the harmonic content independently of the pitch of the tone.

Abstract: In a musical instrument having one or more tone generators in which a plurality of data words corresponding to the amplitudes of a corresponding number of evenly spaced reference points defining the waveform of an audio signal are transferred sequentially from a note register to a digital-to-analog converter in repetitive cycles at a rate proportional to the pitch of the tone being generated, apparatus is provided for simultaneously creating tones at two different pitches. The reference points are computed using specified wave shape symmetry characteristics such that a single variable frequency oscillator suffices to generate both tone pitches without requiring separate, or time shared, tone generation channels.

Abstract: In a musical instrument in which a plurality of data words corresponding to the amplitudes of a corresponding number of evenly spaced points defined a cycle of an audio waveform are transformed at an average rate proportional to the pitch of the tone being generated, a frequency generator is provided using a single master clock source for selectively producing the entire range of musical notes. A non-integer frequency generator is implemented which periodically adds a frequency number, corresponding to an actuated keyswitch, to itself in an adder-accumulator. Overflow pulses from the adder-accumulator address out a set of waveshape values stored in a memory. The noise produced by the unequally spaced overflow pulses is reduced by applying optimal amplitude weighting values to the output waveshape values and then adding the weighted values to provide a single value which is converted to an analog signal and furnished as the musical signal.

Abstract: In a musical instrument having one or more tone generators in which a plurality of data words corresponding to the amplitudes of a corresponding number of evenly spaced reference points defining the waveform of one cycle of an audio signal are transferred sequentially from a note register to a digital-to-analog converter in repetitive cycles at a rate proportional to the pitch of the tone being generated, apparatus is provided for computing the set of data points in the note register from a set of points defining a quarter cycle of the waveform. The calculation of the quarter cycle of data points is divided into two sets. One set is calculated using the odd-numbered harmonics and the other set is caculated using the even-numbered harmonics. The complete waveform is reconstructed from the two sets during the transfer of data to the note registers.

Abstract: In a musical instrument having one or more tone generators in which a plurality of data words corresponding to the amplitudes of a corresponding number of evenly spaced reference points defining the waveform of one cycle of an audio signal are transferred sequentially from a note register to a digital-to-analog converter in repetitive cycles at a rate proportional to the pitch of the tone being generated, apparatus for loading a new set of data words in the note register without interrupting the transfer of data words from the note register to the converter is provided. The note register is divided into two sections. One section is loaded with data words defining half a cycle of an audio signal. By taking advantage of half cycle symmetry of the waveform, the other half of the note register is loaded at the same time using the same data words in reverse order.

Abstract: In a musical instrument in which a plurality of data words corresponding to the amplitudes of a corresponding number of evenly spaced points defining a cycle of an audio waveform are transferred sequentially from a waveshape memory in repetitive cycles at a rate proportional to the pitch of the tone being generated, apparatus is provided for reducing undesired frequency components resulting from the conversion of the digital signals into analog musical signals. The noise reduction apparatus applies optimal amplitude weighting values to a subset of the stored data words and adds these weighted values together to provide a new single value which is used for the output signal.

Abstract: Apparatus for sequencing an electronic organ through a plurality of different combinations of tone settings utilizes an addressable memory to store each setting combination as a separate addressable word in which each bit of the word indicates the setting of one tone characteristic. The words are read out in predetermined sequence at times controlled by the musician, the bits of each word controlling the immediate setting of all the tone control switches. Any word in memory can be read out at any time on command of the musician independently of the sequencing to establish a selected preset status of the tone control switches. The automatic setting of any tone control switch can be manually overridden at any time and the corresponding bit in associated control word in memory changed accordingly.

Abstract: In a musical instrument having one or more tone generators in which a plurality of data words corresponding to the amplitudes of a corresponding number of evenly spaced reference points defining the waveform of one cycle of an audio signal are transferred sequentially from a note register to a digital-to-analog converter in repetitive cycles at a rate proportional to the pitch of the tone being generated, apparatus is provided for adaptively computing the set of data points in response to values of preselected harmonic coefficients. The computation apparatus advances past all harmonic coefficients of smaller magnitude than a selected threshold thereby reducing the computation time and making the instrument capable of responding to time varying tonal changes.

Abstract: An electronic tone generator of a type in which an audio signal of controlled waveform is generated from a stored master data list of digitally coded words incorporates apparatus for changing the harmonic structure of the waveform with time during the generation of the audio signal. The master data list is computed by generating two data lists of words defining different waveforms and multiplying the two lists together repeatedly while shifting one list relative to the other list by at least one word. The resulting master data list changes with each multiplication following a shift, producing a changing waveform in which the musical frequencies are harmonically related, the waveshape being free of intermodulation distortion.

Abstract: In a musical keyboard instrument of a type having a number of tone generators substantially less than the number of keys, one of the tone generators being assigned to a key when activated, the pitch of the tone generator being set by the particular key, apparatus is provided for maintaining a constant audible loudness level to the listener from the tone generator regardless of the pitch of the tone generator. A plurality of sets of amplitude values are stored in a memory, each set including one value for each key. Each set of values corresponds to a particular loudness level. The envelope amplitude of the tone generator output is controlled to produce the same loudness level for all notes by addressing a set of values according to the selected loudness level and addressing a particular value according to which key is activated. An amplitude value is selected which is then used to control the envelope amplitude of the tone generator output signal.

Abstract: A fixed formant filter for a digital electronic instrument of the type in which musical tones are generated from waveshape data calculated independently of frequency of the tone from constituent generalized Fourier components. The Fourier components are individually scaled by scale factors selected from a set of stored scale factors which define the transfer characteristic of the fixed formant filter. Each separately addressable stored scale factor corresponds to a different frequency value in the musical scale. A scale factor is selected for separately scaling each harmonic of the tone generated in response to the particular note of the musical scale keyed on the instrument. The selected scale factors may be modified by a frequency deviation signal to provide vibrato or other frequency modulation effects.

Abstract: A polyphonic tone synthesizer in which two or more distinct voices are sounded by operation of a single key. While the voices have the same fundamental frequency, they are made audibly distinct by differing in harmonic content and differing in the shape of the envelope of the voice signal. The two or more voices are synthesized by alternately calculating master data lists of the amplitude values representative of points on the waveforms of the two voices, adding the two master data lists and converting the resulting values to an analog waveform by feeding the data to a digital-to-analog converter at a rate determined by the fundamental frequency of the note. The master data list for each voice is calculated repetitively during the time the key is operated by multiplying a set of coefficients with a set of sinusoid values and continuously scaling the resultant product by an envelope scale factor which changes with time to correspond to the desired envelope waveform.