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 tones in response to a loudness control signal. Loud tones are produced with a greater number of harmonics than those for a soft tone.

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: 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 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 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: 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: Two sets of digital tone generators are provided for a musical instrument. The members of the first set of generators create data which represent discrete amplitudes of a musical waveshape corresponding in the time domain to be true musical frequencies played by the musician. The members of the second set of generators create data which represent discrete amplitudes of a different waveshape corresponding in the time domain to frequencies which in general are note selected as true musical frequencies. Provision is made for multiplying the data created by selecting pairs of digital tone generators, one from each of the two sets. The resulting modulated data is converted into analog signals in a form suitable for a conventional sound system.

Abstract: Musical notes having time variant modification of the waveshape are produced polyphonically in a tone synthesizer by computing master and transient data sets, transferring these data to buffer memories, adding the data read out from the buffer memories briefly during a transient time interval and repetitively converting the summed data to waveforms. The master and transient data set are created repetitively and independently of tone generation by computing a generalized Fourier algorithm using stored sets of generalized Fourier coefficients. Circuitry is disclosed for independently applying Attack/Release modulations to the principal tone generated from the master data set and to the transient tone generated from the transient data set.

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: 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: 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: 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.