Abstract: An electronic digital type organ having one or more keyboards generating two or more harmonically related tones in response to keying a melody monophonically on one of the keyboards. The harmonic tones may be of different tonal quality, so as to produce the effect of different instruments. The harmonic tones are generated automatically at a pitch determined by either the next lowest note to the accompaniment notes played on another keyboard or, if no other key is depressed, a pitch that is determined by the melody note and stored half-tone interval information.

Abstract: An ensemble effect is produced in a digital tone generator by providing a master data set of words having values corresponding to the relative amplitudes of equally spaced points along one cycle of the waveform of the audio tone. These values are transferred sequentially during repetitive cycles at a rate proportional to the pitch of the desired musical tone to a digital-to-analog converter for converting the master data set to an audio signal of the desired waveform and pitch. The ensemble effect is produced by transferring the words of the master data set to a second converter at the same pulse rate but having one value deleted or repeated once in the second set. Because the second set :has one less or one extra value in the set, the resulting audio tones from the two sets change phase with each successive cycle of the audio signals.

Abstract: An echo effect in a polyphonic digital tone synthesizer in which a musical tone is repeated at a controlled repetitive rate but decreasing peak amplitude when a key is depressed. The tone is repeated until the peak amplitude decays to a predetermined level regardless of when the key is released. If the key remains depressed, the peak amplitude decay recycles so that an echo effect will be repeated. The echo effect is obtained on a plurality of overlapping notes that need not be keyed in unison. The echo control includes an echo envelope register which stores a control word for each key that is depressed. The control word includes bits coded to identify the current amplitude of the echo decay envelope. The value of the control word is decremented at a control rate to provide a decaying echo amplitude. An echo delay register stores a control word for each key depressed, the control word being incremented at a controlled rate.

Abstract: An electronic tone synthesizer in which a master data list of digital values representing the amplitudes of points defining the waveform of a musical tone are transferred to a digital-to-analog converter at a rate proportional to the pitch of the tone being generated. Noise is superimposed on the musical tone by means of a random binary signal generator which controls a circuit for modifying selected ones of the digital values as they are transferred from the master data list to the converter. Modification of the selected values may be by a right shift operation, a 2's complement operation, or by selective delay.

Abstract: A fixed formant filter for a digital tone generator uses a set of scale factors generated by storing in memory a set of words corresponding to the relative amplitude of points on a single resonance curve. The words are addressed and read out of the memory in sequence in response to a counter. For each output state of the counter a group of words is read out of the memory, added, and stored as one scale factor of said set of scale factors. The number of words in the group read out corresponds to the number of resonant peaks in the fixed formant filter. The respective words in the group are addressed by modifying the output of the counter respectively by four constants corresponding to the relative position in the musical scale at which the resonant peaks of the formant filter occur.

Abstract: An automatic arpeggio for a keyboard-operated instrument in which a tone generator is assigned to a key when the key is actuated, the fundamental frequency of the assigned tone generator being determined by octave and note data stored as a control word in a memory in response to operation of the key. On keying the different notes of the arpeggio chord on the keyboard and activating an arpeggio Load switch, a control word is loaded in the memory for each key of the arpeggio chord, the words being coded to identify the value of the note and the sequence number of the note in the arpeggio chord. The arpeggio chord control words in memory are transferred one at a time to a tone generator in a sequence according to the stored sequence numbers of the control words. Arithmetic means, in synchronism with an arpeggio clock, generates note sequence numbers by which the control words are addressed in memory. The note value is transferred to the tone generator together with octave information from the arithmetic means.

Abstract: A tone synthesizer generating a marimba effect in which two percussion notes are sounded alternately an ocatve interval apart, simultaneously with and in response to the playing of a sustained note by depressing a key. The marimba tones are synthesized by alternately, at controlled intervals, calculating master data lists of the amplitude values representative of points on the waveforms of the two marimba tones and converting the respective master lists to analog waveforms by feeding the data in series to a digital-to-analog converter. The master data list for each tone in calculated by multiplying a set of coefficients for each tone with a set of sinusoid values. The coefficients correspond in value to the relative amplitudes of the harmonics of the tone. By sounding one set of coefficients with the odd number harmonics all equal to zero, the two resulting tones sound an octave apart.

Abstract: A transposing and intramanual coupling control circuit for an electronic keyboard instrument in which the status of the keys are scanned in groups by a group counter, each group corresponding to the twelve notes of an octave. The keys in each group provide status signals on a corresponding number of time-shared output lines as each group is scanned. If any key in a particular group has changed status, the scanning of the groups is interrupted and the individual keys in the particular group are scanned by a note counter to determine which keys have changed status. If a key has been depressed, the note number and octave number in the respective counters are stored in an assignment memory for assignment to a tone generator. Transposition is provided by shifting the phasing between the key scanning by the note counter relative to the output lines by a predetermined set amount at the start of each group scanning step.

Abstract: There is described a tone generator in which waveform amplitude data is generated from a table of sinusoid values in an addressable memory by changing the addresses as a function of time in a periodic or sinusoidal manner. The effect is to produce a sequence of sinusoidal values from the table which correspond to a series of points on a frequency modulated carrier signal. By making the effective modulation frequency equal to the carrier frequency, the resulting frequency modulated signal corresponds to a carrier with side bands that correspond to harmonics of the carrier. The relative amplitudes of these harmonics can be varied as a function of time to produce the sliding formant effect of a synthesizer.

Abstract: A tone synthesizer in which a musical tone of selected fundamental frequency is generated with a resonance effect at selected harmonics of the tone. The resonance effect is produced by adding an amplitude modulated carrier signal to the musical tone, the carrier signal being modulated by a signal having the fundamental frequency of the musical tone and the carrier frequency being an integral multiple of the fundamental.

Abstract: A sequence generator for a polyphonic tone synthesizer in which a repetitive sequence of musical notes or chords are generated automatically. During a Code mode of operation, each key operated on the keyboard causes an associated data word identifying the specific key by keyboard, octave and note to be stored in a memory. Time data as to the relative time the note is to go on and go off is also stored as part of the data word. During a Play mode of operation, the data words are read out of memory in the sequence in which they were generated. The words are decoded and the time data compared with a real time clock to provide signals to the output of the keyboard which duplicate the signals from the corresponding keys. The time duration of these signals is controlled by the time on and time off data to duplicate the required time that the respective notes are to be played.

Abstract: A keyboard operated tone synthesizer with glissando effect in which actuating individual keys successively on a keyboard produces all the intermediate notes of the chromatic scale. The time interval between notes in the scale is independently controllable. In one modification of the invention the individual notes of the chromatic scale played during the glissando, when played slowly enough to be heard individually, can be controlled in attack, decay, sustain and release characteristics. The chromatic glissando can move either up or down the scale, depending upon the pitch of each key relative to the previous key played on the keyboard.

Abstract: A sustained repeat control in a digital polyphonic synthesizer for gradually decreasing the amplitude of one or more notes generated repetitively in response to operation of a single key. The sustained repeat control includes a digital register storing a plurality of control words in digitally coded form, there being one control word assigned to each note being generated at any one time. Each word includes bits coded to indicate the current relative amplitude of the associated note. When a key is depressd, the control word or words for the note or notes assigned to that key have bits initialized to a predetermined value. When the key is released the amplitude values represented by the bits are counted down periodically. The bits in turn control the amplitude of the repetitively generated notes, a zero detector terminating the operation when the bits are decremented to zero.

Abstract: An amplitude curve generator for use with an electronic organ or the like to control the musical shape of an audible tone. The generator utilizes a simple binary down counter driven from a clock source to produce a sequence of decreasing binary numbers that approximate the relative amplitudes of equally spaced points along an exponential decay curve. The count condition of the least significant bits of the counter correspond to the mantissa of number expressed in binary floating point notation. The most significant bits represent the power. The bits of the mantissa are transferred to a parallel shift circuit and shifted a number of times determined by the bits of the power to convert the number in the counter to fixed point notation. The output of the shift circuit is used to control the envelope amplitude of a musical tone. The output may be subtracted from one (2's complement) to produce a set of values that correspond to an exponential attack curve rather than a decay curve.

Abstract: A keyboard operated polyphonic tone synthesizer which is touch responsive to the force applied to the keyboard mechanism. Operation of a key operates through a pneumatic transducer to provide an air stream having a velocity proportional to the force applied to the key. A transducer responsive to the velocity of the gas produces an output pulse having a peak amplitude proportional to the peak velocity of the air. This voltage in turn is used to control the peak amplitude of a musical tone generated in response to the operation of the key so that a direct relation exists between the force with which the key is operated and the amplitude of the resulting sound generated by the instrument.

Abstract: A frequency generator for a keyboard operated electronic music instrument using a single master clock source for selectively producing all the notes of the musical scale. A set of frequency numbers corresponding to each of the notes of a diatonic scale are stored in a memory. A frequency number is selected from the stored numbers according to the note to be generated when a key on a keyboard is activated, the selected number being applied to an adder-accumulator periodically at the master clock rate for incrementing the contents of the accumulator. Overflow pulses from the adder-accumulator shift amplitude values sequentially from a set of values stored in a shift register through an adder to a digital-to-analog converter. The adder modifies the amplitude values by applying a fractional part of the incremental difference between each value and the next value in the sequence to the adder. The fractional amount is determined by the content of the adder-accumulator and changes with each master clock pulse.

Abstract: A noise suppression circuit for digital tone generator in which a table of digitized data points are converted at a rate controlled by the fundamental frequency of the tone being generated. The suppression circuit determines the difference between each pair of successive data points and increments the prior data point in a succession of equal intermediate steps proportional to said difference. The data points together with the succession of incremented values between said data points are converted by a digital-to-analog converter at a converter rate equal to or greater than the maximum rate at which each data point is incremented.

Abstract: A digital computer organ in which individual tones are generated by calculating digital data corresponding to the amplitudes of a plurality of sample points within each cycle of the waveform of a selected tone by summing for each point the product of a digitally stored coefficient value and a sine value for each of a predetermined number of harmonics. An addressable memory stores at least one set of digitally coded coefficient values. A coefficient value is read out of the memory for each calculation. The addressing of coefficient values in the memory is under the control of a plurality of multipole switches in the form of drawbars, each position of a drawbar corresponding to an address location in the memory. The drawbars are activated in sequence so that each one selects in sequence the next coefficient value read out of memory according to the setting of the drawbar.

Abstract: An automatic chord generating circuit for a digital polyphonic tone synthesizer having one or more keyboards. Key operated switches are connected in groups corresponding to the notes in an octave. A signal source is selectively connected by the closed switches of each group in sequence to associated ones of a plurality of signal lines. A priority circuit selectively connects a signal from only one line at a time to a corresponding one of a plurality of output lines, so that operation of more than one key in an octave produces only one output signal at a time. A switching logic circuit, responsive to digitally coded input signals identifying any one of a plurality of different chords, connects the single output signal from the priority circuit to additional ones of the output lines for activating multiple notes within the octave.

Abstract: A keyboard instrument having key-operated switches connected in groups corresponding to musical octaves. The groups of keys are pulsed sequentially to provide successive patterns of pulses on parallel time-shared output lines, each group of keys having its own time slot by which the octave of the notes is identified. The pattern of pulses during each time slot identifies the notes within the octave that are to be generated. A repeat signal generator periodically modifies or interrupts the pattern of pulses during the associated time slot. The pattern of pulses may be in effect interrupted as to the keyed note by shifting the pattern of pulses to an adjacent time slot corresponding to another octave for repetitively generating the same note alternately in two octaves.