Abstract: A musical ensemble effect results when two tones slightly out-of-tune with respect to each other are sounded together upon selection of a single instrument key. Herein, apparatus is disclosed for producing an ensemble effect in a polyphonic tone synthesizer of the type wherein musical notes are produced polyphonically by computing a master data set, transferring data set to buffer memories, and repetitively converting in real time contents of memories to notes. A multiplicity of master data sets are created repetitively and independently of tone generation by computing a generalized Fourier algorithm using stored sets of generalized Fourier coefficients. The phase of such master data sets are generated with time varying phase shifts to provide theout-of-tune ensemble effects. The phase shifted master data sets are combined and transferred to buffer memories from which such data is converted to musical sounds.

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: A keyboard operated tone synthesizer with portamento effect in which each key controls the pitch of the generated tone through a table of frequency numbers, each key selecting a corresponding frequency control number from the table and converting this number to an analog voltage which is applied to a voltage controlled oscillator, the oscillator in turn controlling the pitch of the associated tone generated by the synthesizer. The portamento effect of having the pitch of one note slide smoothly into the pitch of the next note is achieved by subtracting the frequency number of a new note to be generated from the frequency number controlling the frequency of the note currently being generated. A fraction of the difference is stored in an increment register and added over and over to the frequency number of the current note at a controlled rate until the frequency control number equals the frequency control number of the new note.

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: Musical notes are produced polyphonically in a tone synthesizer or like musical instrument by computing a master data set, transferring data set to buffer memories, and repetitively converting in real time contents of memories to notes. The master data set is created repetitively and independently of tone generation by computing a generalized Fourier algorithm using stored sets of generalized Fourier coefficients. Computations limit tones to audible frequencies, occur at intervals short compared to musical tone periods, and circuitry is included to provide time-varying modulations of the synthesized tonal structure. Synchronizing signals included in the buffer memories provide smooth transition between the master system logic clock and asynchronous tone conversion clocks. A time shared digital-to-analog converter transforms the buffer memory outputs to individual tone channels and provides attack, decay, sustain, release and other amplitude modulation effects.

Abstract: Tone generation in a musical instrument is accomplished by repetitively computing a Fourier algorithm using stored sets of harmonic coefficients. An alterable voice is obtained by optically reading a data card, converting the data to a data format used by the tone generating circuitry, and storing the converted data to be employed as a set of harmonic coefficients. Harmonic coefficient data is encoded on the data card by imprinting columns of opaque areas. The length of each column is measured by sequentially scanning a linear array of light sources. Insertion of the data card in an enclosure automatically initializes the reading circuitry and removing the card causes each opaque data column to be measured in turn and the result converted to a harmonic component.

Abstract: Sliding overtone generation is implemented in a computor organ of the type disclosed in U.S. Pat. No. 3,809,786. In such an instrument, the sampled amplitudes of a musical waveshape are computed in real time by individually calculating the amplitude contributions of the Fourier components constituting the waveshape. In accordance with the present invention, one or more of these Fourier components is evaluated at a frequency which varies with time. The resultant overtone "slides" up or down in frequency between preselected limits at a controllable rate of "slide speed". Unusual tonal effects are achieved.

Abstract: A single amplitude curve generator is time shared amongst a plurality of musical tone generators for controlling their musical shapes. The curve generator creates a wide variety of envelope characteristics by implementing a recursive computation algorithm for selected choices of a single curve shape parameter coupled with the use of a collection of timing clocks used to vary the time intervals associated with the attack, decay, and release regions of the musical tone envelope. Provision is made for forcing the release of a tone generator when a limited number of tone generators have been completely assigned in a keyboard musical instrument and a new note key switch is actuated. Note release signals can be ignored until the amplitude curve generator has completed the attack and decay regions for a given tone generator.

Abstract: In a musical polyphonic tone synthesizer, musical waveshapes are produced by voltage controlled oscillators. The analog frequency control voltages are created by converting stored digital numbers to analog voltages. The selection of these digital numbers and their assignment to a plurality of voltage controlled oscillators is controlled by detecting switches actuated on a keyboard. Provision is made for operating the oscillators over the full frequency range of an electronic musical instrument's keyboard. Automatic tuning means is incorporated to adjust the conversion reference voltage for each oscillator to keep the musical instrument in tune by locking the set of voltage controlled oscillators to a stable reference oscillator. Tuning the reference oscillator thereby tunes the set of voltage controlled oscillators while retaining equal tempered musical frequencies.

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.

Abstract: Touch responsive control of note amplitude and harmonic content is achieved by providing each key with a touch responsive transducer. A set of attack/decay scale factors are accessed sequentially from a memory and used to establish the amplitude envelope of the generated note. The accessed scale factors are modified by the transducer output to effectuate touch responsive amplitude control. In a preferred embodiment, scale factors stored in consecutive memory locations define a piano-like attack/decay envelope. The transducer output sets the initial memory access location, so that the harder the key is struck, the greater the initial amplitude of the generated note.Other embodiments include touch responsive control of the constituent Fourier components of the generated tone; and utilization of multiplexing for time shared connection of plural analog touch responsive transducers to a single analog to digital converter.

Abstract: A multiplier for multiplying a fixed point multiplicand by a floating point multiplier utilizes decode logic which provides control signals related to two numbers, the sum of which is approximately equal to the mantissa of the multiplier. The multiplicand is separately left shifted in two circuits, responsive to the control signals, by a number of places respectively corresponding to the values of said two numbers. The shift circuit outputs are summed algebraically in an adder. The sum is then shifted by a number of places and in a direction determined respectively by the magnitude and sign of the power of the floating point multiplier. The result is a close approximation of the desired multiplication product. The multiplier advantageously is employed in an electronic musical instrument.

Abstract: Keyboard switches are arranged in groups of P switches, Q groups per set, and S sets per keying system. During a search cycle, each group of P switches is sequentially examined to detect a change in a switch state of any member since the preceding search cycle. A change in switch state causes system to enter an assign mode cycle during which a data word is created in memory corresponding to a newly detected switch closure, or is removed from memory corresponding to a newly detected switch opening. Provision is incorporated for coupling between switch groups and switch sets. After an assignment has been completed, system returns to a search cycle. The system is particularly useful in a keyboard musical instrument.

Abstract: In this key switch scanning and encoding system, open (OFF) switches may be scanned at a faster rate than closed (ON) switches, and a coded signal is produced indicative of each closed switch. The switches are arranged in a matrix of M groups each connected to N common output lines. The switch groups are enabled sequentially, one at a time. As each group of switches is enabled, the N output lines sequentially are gated to a coding matrix. If the gated line is associated with a closed switch in the enabled group, an output code is produced by the code matrix, which, together with a signal designating the enabled group, uniquely identifies the closed switch. Scanning is delayed briefly to permit utilization of the encoded output. If an open (OFF) switch is scanned, no code is produced by the code matrix. This no-code condition immediately causes the next switch matrix output line to be gated to the code matrix. In this way, open switches are "skipped over" or scanned at a rapid rate.

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.

Abstract: Formant filtering is implemented in a computor organ of the type disclosed in U.S. Pat. No. 3,809,786 by eliminating, attenuating or accentuating certain Fourier components included in each waveshape amplitude computation. A set of formant filter factors define the formant filter passband as a function of frequency, logarithmic frequency or Fourier component order. As each constituent Fourier component is independently evaluated, the component amplitude is scaled by the appropriate formant filter factor. The resultant synthesized musical tone includes only Fourier components within the defined passband, so that formant filtering effectively is implemented without the use of an actual filter.

Abstract: Timing signals of adjustable rate are estabilished digitally in an electronic musical instrument through the use of digital timing numbers. A selected one of such numbers is repetitively added to the contents of an accumulating adder at a fixed rate. A train of timing pulses is obtained from one bit output of the adder; the rate of these pulses is directly related to the value of the selected timing number. Alternatively, consecutively updated parallel bit timing codes can be obtained from plural bit outputs of the accumulating adder. These timing codes, which are incremented or decremented in value by amounts established by the selected timing number, are useful for directly addressing a memory containing a set of musical instrument factors that are to be utilized on a time dependent basis.

Abstract: Delayed vibrato is implemented in an electronic musical instrument of the type wherein the fundamental frequency of the generated tone is proportional to a frequency number R supplied to the instrument. At the beginning of note production, the frequency number R itself is supplied to the instrument for a preselected delay time, so that no vibrato is introduced during this initial delay time. Subsequently a periodically varying fractional frequency number R.sub.v is added to the frequency number R and the sum supplied to the instrument. This causes the generated tone to exhibit vibrato at a rate corresponding to the periodicity of the value R.sub.v. The depth of vibrato is established by the maximum value of R.sub.v and may be varied by scaling R.sub.v. Advantageously such scaling is done when the vibrato begins, so that the vibrato depth will increase gradually to the maximum value.