Time shared tone keying system in electronic musical instrument

Abstract

In an electronic musical instrument, a tone source circuit provides tone signals of audio frequencies representing respective notes in a musical scale. A keyboard circuit provides a keying sequence pulses each existing at such a time slot of time sharing at an ultra-audible rate as is assigned to each of keys being depressed. The tone signals and the respectively corresponding keying sequence pulses are AND-gated respectively and then OR-gated commonly to produce a combined tone signal. The keying sequence pulses are obtained by sequentially scanning all the keys in the keyboard in one sequence, or may be equivalently obtained by scanning the same named keys in different octaves simultaneously and AND-gating with octave representing pulses. Or the octave representing pulses may be omitted by separately processing tone signals octave by octave. The system is suitable for digitalization and for production in IC configuration.

What is claimed is: 
     
       1. An electronic musical instrument comprising: a tone source signal generator for simultaneously generating a plurality of square wave tone signals, each of an audible frequency corresponding to a respective note of a scale having several octaves and each on a separate output of said tone source signal generator;   a sequence pulse generator having a plurality of separate outputs, each corresponding to a respective separate output of said tone source signal generator, said sequence pulse generator being operative in repetitive cycles to sequentially produce in each cycle a respective sequence pulse at each separate output thereof in the order of sequence of the notes of said scale, the sequence pulses produced at each said separate output having an ultra-audible repetition frequency;   a plurality of AND circuits equal in number to the number of separate outputs of said tone source signal generator, each AND circuit being directly connected at its input to a respective one of said tone source signal generator outputs;   a key switch circuit including respective key switches for each note of said scale, each key switch being operable upon depression of its associated note key to connect the corresponding separate output of said sequence pulse generator to the input of the AND circuit to which the corresponding separate output of said tone source signal generator is directly connected, whereby each AND circuit will pass to its output all sequence pulses received at its input from said sequence pulse generator by way of said key switch circuit during the duty cycles of the tone signal received at the AND circuit input; and   an OR circuit connected in common at its input to all of the outputs of the respective AND circuits for combining the sequence pulses at all said AND circuit outputs and thereby obtaining at the OR circuit output a train of tone signal pulses corresponding to the depressed keys.   
     
     
       2. An electronic musical instrument as defined in claim 1 which further comprises a low pass filter circuit for receiving the output signals of said OR circuit and removing the high frequency pulses included in said output signals. 
     
     
       3. An electronic musical instrument comprising: means for sequentially and individually generating note pulses occupying different time slots from each other within one octave;   means for sequentially and individually generating octave pulses occupying different time slots depending upon the kind of octave, each time slot being equal to a period of time for one octave of said note pulses;   a keyboard matrix circuit for connecting key switches for repective keys to a plurality of column lines and row lines corresponding to the notes and octaves of the keys, causing each note pulse to be applied to a corresponding one of said column lines and producing outputs from said row lines upon depression of the keys;   a tone signal generator for producing frequency signals corresponding to the notes of the keys and having periods accommodating said different time slots of said octave pulses; and   a plurality of AND circuits each being provided for a corresponding one of said keys each AND circuit receiving at its inputs said output from a key switch and said frequency signal corresponding to the note of the key, and, upon depression of the key, periodically producing a note pulse corresponding to the key in joint response to the output of said row line, an octave pulse representing the kind of octave to which the key belongs and a frequency signal corresponding to the note of the key, whereby a tone source signal corresponding to the depressed key is produced from said AND circuits.   
     
     
       4. An electronic musical instrument as defined in claim 3 which further comprises a plurality of OR circuits each being provided for one of respective keyboards and receiving the outputs of the AND circuits provided for the same keyboard for controlling tone color and volume of the tone source signal by each keyboard. 
     
     
       5. An electronic musical instrument comprising: means for sequentially and individually generating note pulses occupying different time slots from each other within one octave;   a keyboard matrix circuit for connecting key switches for respective keys to a plurality of column lines and row lines corresponding to the notes and octaves of the keys, causing each note pulse to be applied to a corresponding one of said column lines and producing outputs from said row lines upon depression of the keys;   a tone source signal generator for producing frequency signals corresponding to the notes of the keys and having periods accommodating said different time slots of said note pulses; and   a plurality of AND circuits each being provided for a corresponding one of said keys each AND circuit receiving at its inputs said output from a key switch and said frequency signal corresponding to the note of the key, and, upon depression of the key, periodically producing a note pulse corresponding to the key in joint response to the output of said row line, a note pulse representing the note of the key and a frequency signal corresponding to the key, whereby a musical tone waveshape is produced on the basis of the note pulse periodically selected in said AND circuit.   
     
     
       6. An electronic musical instrument as defined in claim 5 which further comprises a plurality of OR circuits, each being provided for one of the octaves and receiving the outputs of the AND circuits provided for the same octave for controlling tone color and volume of the tone source signal by each octave. 
     
     
       7. An electronic musical instrument comprising: a plurality of AND circuits and key switches, each AND circuit and key switch corresponding to a respective one of a plurality of musical pitches in a pitch range spanning a plurality of octaves having like pluralities of notes, each AND circuit producing and AND-logical output signal upon receipt of first, second, third and fourth input signals in a predetermined time relationship;   a tone source signal generator for providing said first input signal as a sequence of tone pulses of a first time duration occurring at an audible repetition frequency according to the frequency of said respective one of said plurality of musical pitches;   an octave pulse generator for providing said second input signal as a sequence of octave pulses of a second time duration substantially less than said first time duration and occurring in a time slot of said tone pulses which is allocated exclusively to the octave of said respective one of said plurality of musical pitches;   a note pulse generator for providing said third and fourth input signals as identical sequences of note pulses of a third time duration substantially less than said second time duration and occurring in a time slot of said octave pulses which is allocated exclusively of the note of said respective one of said plurality of musical pitches, said fourth input signal being received by the AND circuit corresponding to said respective one of said plurality of musical pitches only upon actuation of the key switch which also corresponds to said respective one of said plurality of musical pitches; and   means for adding together all the AND-logical output signals produced by said AND circuits to thereby provide a composite tone signal having an audio frequency component substantially the same as that which would be formed by superimposing upon one another the tone pulse input signals of the AND circuits having actuated corresponding key switches.   
     
     
       8. An electronic musical instrument comprising: a note pulse generator having a plurality of separate outputs, each corresponding to a respective note of one octave, said note pulse generator being operative in repetitive cycles to sequentially produce in each cycle of its operation a respective note pulse at each separate output thereof in the order of sequence of the notes in said octave, the note pulses produced at each separate output of said note pulse generator having an ultra-audible repetition frequency;   an octave pulse generator having a plurality of separate outputs, each corresponding to a respective octave of a plurality of octaves, said octave pulse generator being operative in repetitive cycles to sequentially produce in each cycle of its operation a respective octave pulse at each separate output thereof, the octave pulses produced at each separate output of said octave pulse generator having an ultra-audible repetition frequency and a pulse width equal to the period of one operating cycle of said note pulse generator;   a tone source generator for simultaneously generating a plurality of square wave tone signals, each of an audible frequency corresponding to a respective note in a respective octave and each on a separate output of said tone source signal generator;   a plurality of AND circuits equal in number to the number of separate outputs of said tone source signal generator, each AND circuit being directly connected at its input to a respective one of said tone source signal generator outputs, while each separate output of said note pulse generator and each separate output of said octave pulse generator are directly connected to those AND circuit inputs that are directly connected to a corresponding separate output of said tone source signal generator;   a key switch matrix circuit comprising a plurality of column lines and a plurality of row lines, each line of one plurality of lines being connected to a respective one of said separate outputs of said note pulse generator for receiving the note pulses produced thereat, each line of the other plurality of lines corresponding to one of said plurality of octaves and being directly connected to the input of each AND circuit whose input is already directly connected to receive a square wave tone signal corresponding to a note in said one of said plurality of octaves, and a plurality of key switches, one for each note in each octave and each operable upon depression of a respective key to connect a particular line of said one plurality of lines to a particular line of said other plurality of lines, thereby supplying note pulses corresponding to the note of the depressed key to the input of an AND circuit already being supplied at its input with note pulses, octave pulses and a square wave tone signal, all corresponding to said note, from the respective generators, said AND circuit only passing to its output those note pulses which occur both during the pulse times of the octave pulses and during the duty cycles of the square wave tone signal; and   an OR circuit connected in common at its input to all of the outputs of the respective AND circuits for combining the note pulses at all said AND circuit outputs and thereby obtaining at the OR circuit output a train of tone signal pulses corresponding to the depressed keys. .Iadd. 9. A time division multiplexed keyboard musical instrument, comprising:   a keyboard having keys each corresponding to a musical note,   a multiplexed tone source means for producing a time division multiplex signal having a plurality of time slots corresponding to said keyboard, each of said time slots being allocated to a corresponding individual key of said keyboard, said signal in each of those time slots corresponding to selected keys consisting of amplitude samples of a harmonic-rich tone source waveform having a note frequency designated by the individual selected key allocated to that time slot, there being no amplitude samples in the remaining time slots which correspond to non-selected keys,   a single format filter connected directly to receive said time division multiplex signal, said single formant filter controlling the frequency components of all of the time division multiplexed tone source waveform amplitude samples and providing as an output a musical tone signal having a predetermined tone color, and   an audio system receiving said musical tone signal and producing corresponding audio musical sounds therefrom. .Iaddend.