US3702370A - Digital tone generator system for electronic organ employing a single master oscillator - Google Patents

Abstract

For use in electronic organs and the like, an electronic circuit for generating a number of signals, the frequencies of which may correspond to the notes of the musical scale, comprises a single master oscillator producing an alternating signal coupled to a harmonic pulse frequency generator producing a number of harmonically related pulse frequency outputs which are selectively connected to summing means, each summing means producing a single output frequency which corresponds to a note of a musical scale. Twelve summing means may be connected selectively to produce the twelve notes of a musical scale.

Description

11,51 14s]- Nov; 7,1972

1 1541 TDQIIGITAL TONE GENERATOR SYSTEM- FOR ELECTRONIC ORGAN 1 EMPLOYING ASINGLE MASTER 1 OSCILLATOR 1 1 I v [72] Inventor: John Ray Hallman, Jr., Green Banlc,

' W. Va. 24944: I 1

221' Filedi May 19,1971

211 Appl. No.:144,874

52] -U.s c1.... ...s4/ 1 .0 1,-s4/1'.04,84/111,

. V .84/1. 19, 84/1.22,84/124 s1 1 11.c1...; .'.G1 0h1/00 [58] Field of Search ......84/1.01, 1.03,1.11,1.17,

84/125, DIG.11, 1.19; 307/225, 226; 1

I FOREIGN PATENTS OR APPLICATIONS 1' 1,213,210 3/1966, Germany; ..s4/1.03

OTHER PUBLICATIONS I Richard Phillips, Many Digital Functions 'Can Be Generated, Electronic Design 3, Feb. 1 1968 pages Primary Examiner-Richard B. Wilkinson 7 Assistant Examiner-U. Weldon [571 ABSTRACT For use in electronic organs and the like, an electronic circuit for generating a number of signals, the frequem cies of which may correspond to the notes of the musi- 1 cal scale, comprises a single master oscillator produc- 331/5l,53 ing an alternating signal coupled to a harmonic pulse i frequency generator producing a number of harmoni- [56] References Cited cally' relatedpulse frequency outputs which are selec- 1 1 tively connected to summing means, each summing I D STATES PATENTS 1 means producing a single output frequency which cor- 3 509 454 4/1970 1 Gossel 84/1 i X responds to a note of a musical scale. Twelve summing 1 means may be connected, selectively to produce the 3,617,901 11/19 71 Franssen ..84/1.01 X twelve notes of amilsical Scale 3,590,131 6/1971 Reyers.....-... V ..84/1.03 I 1 3,601,518 8/1971, l lill;. ..84/,l.l.9 6 Claims, 7 Drawing Figures r CRYSTAL 1 (Y --B|, 822E311 DIGITAL (W PULSE A. cmrsm. HARMONIC {V FREGUFNc YG G1 1?." MASTER I u 1 OSCILLATOR PULSE SUMMING q 1 I Fm CRYSTAL GE'NERATGR k5 GATES F, MASTER a B OSCILLATOR F 2 KP V D11.

. k 17. VOLTBGE p I P 56 1 14 com-amen (D 1 -M F a lfsiilfils k ANALOG 1 INHIBIT VOLTAGE CONTROL cowraou INPUT 'mPuT r {m nim #1 m 12 MASTER Y OSCILLATOR I MAST-ER \4- CONTROLLED K I.

\'NPuTf 3702.370 "sum 1pm I -f n I D IGlTALI PULQE A HARMONIC FREQumcY%C-}fl MASTER oscuu'nma CRYS AL PULSE K 1 summmo RYSTAL Q 6ENE ATQ LVFE M' Q ra vomoa ANAL I I QYIAIIHIQBIT -voLTn6E I 1 CONTROL CONTROL. mpur INVENTOR" 61w www DIGITAL ,TONEGENERATOR SYSTEM FOR-1 I 'ELECTRONIC.ORGAN EMPLOYING A SINGLE- 5 MASTEROSCILLATOR- v .The ,presentinvention relates generally to electronic organs and more particularly to the p'roductionof the supersonic or high f requency signals corresponding .to

\ the twelve notes of'the'musical scale used in someelectronic organ'systems. v v t ln 'the usual tone generator of anelectronic-organ, an

} array of 12 master oscillators is provided which operate.

at. high audio-or supersonic frequencies. These oscillators each drive a chain of octave dividers producing the 1 the organas will become apparent after the invention is completely described. Also, thepulse widths produced bythe'DHPG' are very narrow The pulse width is chosen to be equal-to about one-half the period of the frequency that results from'thearithmetic sum of the values of all the frequency; outputs of the DHPG. The

' description .of the ".pulseffrequency summing gates should make this clear. lo the invention the. pulse octaves'of the notes. In accordance with thepresent invention on .theotherhand, only one master oscillator is required. This oscillator iscoupled a digitallhar; monic pulse generator (DHPG): that produces a. multiplicity of harmonicsof the masteroscillator. The harmonics produced are fixed by the'organ designer and I I may be chosen for convenience of design as well as economy. The various harmonics produced in a-DI-IPG are selectively-summed in a digital 'or' gatepulse summing scheme to produce the l2 frequencies of .the

notes of amusical scale,the octave of which is chosen I by the designer but i's'usu'ally a high octave in theupper range. of human hearing ability. It may.,-'actually, be higher than the range ofhuman hearing and usuallyis.

Each of these notefrequencies is connected to'a'con- I ventional octave divider chain producing the, lower octaves of. each note. Thus, the whole gamut of note frequencies maybe produced.

j The whole system is digital in nature and hence, is well defined. the science of large scale integration in packaging circuits advances,'it will soon bepossible to v package. the entire integrated circuit into a single chip with a multiplicity of leads connectingto the mechanical parts of the organ. So the entire digital electronic circuitmay be packaged into anintegratedfcircuit 'allowinggreat economy in building electronic music in-.

struments. Thisinvention of thefpresent application also improves the tuning stability of the organ since only one oscillator is required withall'other frequenciesbeing digitallyrelated tothe one master oscillator.'

3, In further accordance with. I frequency" summing gates (PFSG) are provided to' selectivelysum theoutputs of-toDI-IPGf ThePFSG performs an arithmetic addition of the -Dl-IPG outputs similar to the following simplifiedexample. ,If we have a DHPG to whichhas been connected an oscillator at a frequency of 8 hertz and further, the DHPGis binary so I that it'producesthe harmonic pulse frequencies of 4 hertz,- 2 hertz, and l hertz; then we may obtain the.

frequency of hertz'by using-a digital or gate to add thetwo, DI-IPG outputs of '1 ,and'4 hertz. In fact,we may 3. obtain anyofthe frequencies l, 2, 3, 4, 5,6, or7'hertz thisway; Notethat 7; hertz is l hertz less thanlthe oscillator frequency of 8 hertz. One hertz is equal to the least significant bit of the DI-IPG where each of the output frequencies of the DI-IPQ are referred to as bits. It can be seen that the choiceof theDI I'PGoutput pulse width of one-fourteenth second is optimumbecause this provides an approximately 50 percent duty factor at the PFSG output for 7'hertz which further assures that no DIIPG output pulses occur at the same instant of time which would cancel pulses, there by causing freq'uencyerrors. For the case where the tone genera tor system operates from the output of a, voltage controlled oscillator the pulse width mentioned above should be selected" after considering the. highest frequency output of the voltage controlled oscillator. In

order that this invention. produce the 12 frequencies'of the notes of the scale, it'is necessary that theD I-IPG have more than three bits." The actual-quantity is dependent onthe frequency of the masteroscillaton'the type of cooling or harmonic relationship of the outputs of theDI-IPG, and the precision of the musical note i In accordance withtheinvention, a master oscillator I is provided with a frequency-(Fe) several times higher than thehighestnote played on the organ. Fo depends on several factors, namely; ho is chosen to minimize the required structure of the pulse summing gates, Fo

, must be chosen high enough above the highest note on the organ so that the unwanted harmonic content (phase jitter) of this note is minimized to an acceptable level, and other factors, all of which become more apparent after consideration of the detailed description of one embodiment of thisinvention. v I In further accordance with the invention, a digital harmonic pulse generator (DHPG) is provided 'to produce the pulse frequencies. Inthe present invention, the DI-IPG produces 12 frequencies. This is pure coincidence with the fact that there are 12 notes in the I must be in the range of the oscillator capability, Fo

frequencies produced. Thisis againa costvs precision tradeoff. The type of coding mentioned above is concerned with the digital codingschemes used in any-conventional digital systems design. Any type coding may be employed but after design considerations it will be found that certain coding schemes are better than others affording more precision at less cost. Some exainples of coding that may be used are 8421 binary, coded decimal, 5411, 5211, l 1 l 1, etc. In the embodiment of the invention presented herethe coding used is 8421 binary which is easily generated from a digital bimusical scale, but any other quantity of pulse frequencies'could be chQsemThere is an optimum quantity thatis a trade off between economy and precision of I frequency of the musical notes that are produced in this 1 organ tone generator system. The more pulse frequencies produced by the DI-IPG, the more precise will be the musical notes and also the more'e'xpensive will be are in the form of phase jitter and very narrow pulses in I the conventional sense. These effectsare divided at the 3 same ratio as frequency is divided in flip flops and octave divider systems. In view of this effect it may be desirable to increase the frequency of the master oscillatorto compensate for a number of stages of division if employed before making available the highest octave outputs from the conventional octave dividers. The

lower octaves are further divided in frequency and hence will contain an even smaller percentage of unwanted harmonics. This organ system employs 12 chains of octave dividers in one application, one for each noteof musical scale. Essentially the invention is intended to replacethe 12 master oscillators usually connected to the octave dividers found in conventional organ designs. The number of stages in the octave divider chain depends on the overall range that the organ is to have. The gamut vof notes of the organ are found at complete organ tone generation system that has as it reference requirement, although not limited to, one master oscillator and that is capable of generatingthe l2 supersonic note frequencies that are usually produced by a set'of 12 master oscillators in most conventional systems.

ltis another object of theinvention to provide a vibrato effect with heretofore unattainable wide frequency modulation range of many octaves by voltage control of the master oscillator when a voltage controlled oscillator is employed'instead of a crystal controlled oscillator.

It is a further object of the invention to provide switch selectable instrument key selection. Organs and pianos usually are tuned in the key of C. But with this inventionby providing more crystal oscillators selected by switch or some other variable oscillator reference,

the organ may be tuned to any other musical key quite easily without the necessary tuning job that would otherwise'be required.

- by just turning a knob that controls the potential applied to the control terminal of a voltage controlled master oscillator. I

It is a further object of the invention to provide for easily and selecting tuning the organ to other. temperaments such as the just, mean, or pythagorean scales. This embodiment of the invention is mainly shown in this patent application adjusted for the equal temperament scale, however.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein;

FIG. 1 is a block diagram of asystem for generating the 12 high audio or' supersonic frequencies corresponding to the notes of the musical scale. I f n FIG. 2. is a digital harmonic pulse 'gie'neratortDI-IPG) providing 12 harmonically related pulse frequencies, in the system of FIG. 1. j I, t I

FIG. 3 is a group of 12 pulse frequency summing gates for producing the 12 high audio or supersonic musical note frequencies when connected to the outputs of the Dl-IPG of FIG. 2, in thesystem of FIG. 1.

FIG. 4 is a simplified. alternate construction of a digital harmonic-pulse generator (DI-IPG) coupled to a pulsefrequency summing. gate (PFSG); "that. were shownin FIGS.2and 3.

FIG. 5 is a timing diagram sequences of some of the signals in the circuit of FIG. 2.

FIG. 6 is a timing diagram showing the timing sequences of :signals present in the simplified example ofFIG.4: w I

FIG. 7 is an optional'4 octave dividerthat may be employed to improve the purity of the supersonic note frequency outputs of the pulse frequency'summing gates (PFSG).

Referring now to the accompanying drawings, in FIG. 1, the blocks ll, l2, l3, and 14 are all oscillators "nroducing squarewave outputs 15, 16, 17', and 18 compatible with the driving requirements-of the type of digital logic circuits employed in this embodiment of the present invention. In all-examples of the present invention the logic used is transistorrtransistor logic (TTL) integrated circuits. This is not a limitation since any form of logic circuits may be employed in the design of the invention. In conventional TTL circuits the following definitions prevail. A logic 1 is true and a voltage level of approximately plus 5 volts, whereas a logic 0 is false and is a voltage level of approximately ground potential. A plus edge is a logic transition from 0 volts to plus 5 volts, whereas a minus edge is a logic transition from plus Sto 0 volts. A plus pulse is comprisedlof a plus edge followed after'a time interval (pulsewidth) by a minus edge back to ground potential, whereas a negative pulse is comprised of a minus edge followed after a time intervalby a plus edge back to plus 5 volts level. a

The four oscillators areshown switch selectable to allow the organ'to be tuned to a different musical key simply by changing a selector switch. In actual application there may be as many oscillators as the builder desires but there must be at least one oscillator since this is the reference to which all musical notes produced by the invention are referenced. So, with the proper oscillator frequencies chosen, three different musical keys would be allowed by the oscillators 11,

ing a vibrato range of many octaves heretofore not v possible with other organ tone generator systems. In

showing v the timing i fact by playing achord on the organjand then varying the potential "on the control input of the voltage controlled oscillator '14 ina selectiveway music compristo the reference oscillator. For this example of the invention the outputs areplus pulses that follow the binary progression whereby Y is one-halftheoscillator frequency andX is one-fourth'the oscillator frequency and so on until L is 1/4096 0f the reference oscillator frequency. The digital harmonic pulse generator circuit number of special has 19 as I.,M',N,P,R,S,T,U,V,W,X,Y are harmonically related I may be any one of several types of devices without departing fromthe true spirit of the invention.

These pulse frequencies are thenselectively summed by the pulsefrequency summing gates 21,'to produce the supersonicpulsetraini frequencies of the'musical notes of thescale. These pulse trainfrequency outputs are inharmonic since they contain much phase jitter as well as being very narrowpulses.= Theseoutputs maybe made more pure by dividingwith digital 'flip flop circuits before allowing any outputs to reach thelistener. The circuit of FIG. 7 may be used forthis purpose and is optional as how many stages of division to employ. More stages of division will produce more purity of the outputs.

In FIG. 7 the input is C12, for example connected from'Cl2 of FIG. 1. Thedivide' by two circuits26, are flip flops, four stages of which will produce C8 at the output. It may be desirable to increase the master oscillator frequency by a factor of'l'6 thereby'raising the input to C16 following the nomenclature. The output of the circuit of FIG. 17 will then be C12, allowing the full musical range of theorgan. Theseoutputs may then be connected to conventionaloctave divider and harmonic processing tone circuits to providethe gamut of A timing diagram showing the timing sequence of some of the signals present in the digital, harmonic pulse generator of FIG. 21is shown in FIG. 5. Notice that the transitions of 23, 24 and 25 occur during negative transitions of the clock input 19. Also'note further that pulse trains W, X, and Y occur at plus edges of-25, 24, and"23, respectively. This must be arranged this way to assure that no two one-shots are triggered at the same instant which'wo'uld cause their outputs to occur in coincidence, thereby'causing cancellation of some pulses being summed by'the summing gates-rendering frequency summing errors; The important thing is that no two pulses be allowed to occur at the same instant of If a digital or gate has'inputs connected to Wand Y then with a masteroscillatorfrequency of 8' hertz, a frequency of 5 hertz is present at the output of the-or gate since the frequency of Y underthese conditions-is 4 hertz and W is l hertz. The pulse frequencies of W and Y are sumed by theor gate. Z in FIG. 5 shows what the or gate output looks like in time sequence..Note.

that the pulses are not evenly spaced but exhibit a phase jitter. Because of this effect musical notes produced directly from a system such as this are inhar- T monious, since many harmonics not correctly related .to the fundamental are produced. However, this phase jitter may easily be'reduced by dividing through flip flops and increasing the master oscillator frequency to compensate for the division ratio of several flipflops.

FIG. 3 shows a group of 12 pulse frequency summing gates 50 that may be employed in item 21, FIG. 1 to process the outputs of the DI'IPG to produce the high audio or supersonic frequencies corresponding to 12 notes within a single octave range for the organ. The

operation of these or gates is identical to that of the or gate in the precedingparagraph "except that more inputs are present. L,M,N,P,R,S,T,U,V, W,X,,and Y are v inputs to the gatesfrom the DI-IPG of FIG. 2, the pulse frequencies of which are tabulated in table 1. I TABLE 1 g 1' a Fo=780.8 frequencies in hertz Y=390.4

S=6.1 R=3.05 P=l .525 N=.7625 M=.38 125 L=. 190625 V The frequencies shown result if the master oscillator frequency E. is set equal to 780.8 hertz. These frequen- The flip flop outputs drive monostableone shots that trigger on different edges from the flip flops namely the plus edges so that onplus transitions of the outputs of the flip flops there are pulses present at L,M,N,P,R,S,T,U,V,W,X, and Y. These are thepulse frequency outputs of thedigital harmonic pulse generator.

cies may be selectivelyv summed in certain ways to produce theproper frequencies of the 12 notes of the equal tempered musical scale, approximated to an average accuracy of 0.0953 125 hertz. Table 2 is a tabu lation of the exact frequencies of the notes of the musical scale of equal temperament. The summingcom binations are shown on the right side of the table. To

obtain the note G for example we, add Y and as indicated by a l in therespective columns. The note will same.

7 or minus 0.0 hertz. The error will not be noticed by the listener. Accuracy and system costmay be reduced by reducing the number of frequencies generated by the Dl-IPG. More accuracy may be obtained by increasing TABLE 2 For F 780.8 hertz and all frequencies specified in These values of frequencies and combinationsshown in Tables 1 and 2 were obtained from a computer program that minimized pulse frequency summing gate structure vs.- F0 within a small range of F0. It is obvious that a better computer program will generate more combinations for summing pulse frequencies at different F0 frequencies and that this does not depart from the scope and spirit of the present invention.

The inhibits inputs to the gates of FIG. 3 allow them to be inhibited by logic control signal while another gate or set of gates are enabled. In this case all gates producing C12 for example are coupled to the octave dividers and likewise the other eleven may be coupled to the outputs in the same manner. The feature allows special effects and changable temperaments at will. The inhibit input in FIG. 1 serves the same purpose and in-fact, is the same where the inhibit inputs of each gate in'a set of 12 are grouped to this input. A logical high level to this input will inhibit the operation of the PFSG in FIGS. 1 and 3. It is obvious that by computer program or other means a set of pulse frequency summing gates may be designed to produce the just, mean, or pathagorean temperament scales.

A simplified alternate system for producing one frequency of 5 hertz is shown in FIG. 4. In this example a gating scheme is employed instead of the analog monostable one shots to produce the pulses. The operation is similar to the previous example and is included for clarity as well as to demonstrate that there are a multiplicity of ways of building the present inven- While I have described and'illustrated one or two specific embodiments of myinvention, it will be clear that variations of the details of construction which are specifically illustrated and described may beresorted 5 to without departing from the" true spirit and scopeof the invention as defined in the appended claims.

An exact circuit diagram of a modelof the invention along with a description is on file at the" United States I Patent Office and is disclosure document number 5076 10 filedMayl4,l97l. -WhatIclaim is:

l. A tone generating system for an electronic organ comprising a master oscillator means producing a s'quarewave output connected to a-single digital harmonic pulse generating means producing anumber of pulse frequencies connected to a plurality of pulse frequency summing means, eachpulse frequencomprises a plurality of master oscillators set at different frequenciesthereby allowing the organto be tuned by selector switchinstantly to different musical keys by selecting corresponding master oscillators.

2. The combination according toclaim fwherein said master oscillator means comprises a voltage controlled oscillator allowing the musical key to which the organ is tuned to be altered' by varying the potential applied to the voltage control input of the master oscillator, thus allowing the organ toproduce a multiplicity of special effects. I

3. The combination accordingto claim twherein said digital harmonic pulsegenerating meats comprises a chain of cascaded digital flip flop circuits, the outputs of which are coupled to monostable one shots producing the pulse frequencies. r

4. The combination according to claim 1 wherein said digital harmonic pulse generating means comprises a chain of cascaded digital flip flops, the outputs of which are coupled to gating means producing the pulse frequencies.

The nesqqrs ia F9 1a 19. ,wl s: a

' number of ahai'fisbr flip flops of N stages each are connected to each pulse frequency summing means output '50 (and the conventional octave divider chains) and further increasing the master oscillator frequency by a factor of 2" to compensate for the flip flop division ratios thus reducing the undesirable harmonic content of the musical note frequencies appearing at the out- I tion. The oscillator 31 output is an 8 hertz squarewave jipqtspf Said flip flop di e Chains.

connected to a chain of three flip flop divide by twos 26. The inverters 33 invert the sense of the logic signals connected to them. The and gates 32 produce 1, 2, and 4 hertz from top to bottom respectively. the outputs 39 and 41 are summed in or gate 34 to produce the 5 hertz output 42. The and gate output 40 is not needed and hence, is not used to produce 5 hertz. A timing diagram for the signals present in FIG. 4 is shown in FIG. 6. Note that none of the pulses of 39, 40, and 41 occur at the same instant of time.

6. The combination according to claim 1 wherein said master oscillator means comprising a crystal oscillator, saidhigh pulse frequency, each connected to flip flop divider chains producing audio frequencies to which other types of musical instruments may be tuned thus allowing a reference for the tuning pur-

Claims (7)

1. A tone generating system for an electronic organ comprising a master oscillator producing a squarewave output connected to a single digital harmonic pulse generating means producing a number of pulse frequencies connected to a plurality of pulse frequency summing means, each pulse frequency summing means connected to selected pulse frequency outputs of said digital harmonic pulse generating means whereby each pulse frequency summing means produces a single high pulse frequency at its output that is equal to the sum of the selectively connected outputs of said digital harmonic pulse generating means.

2. The combination according to claim 1 wherein said master oscillator comprises a plurality of master oscillators set at different frequencies thereby allowing the organ to be tuned by selector switch instantly to different musical keys by selecting corresponding master oscillators.

3. The combination according to claim 1 wherein said master oscillator comprises a voltage controlled oscillator allowing the musical key to which the organ is tuned to be altered by varying the potential applied to the voltage control input of the master oscillator, thus allowing the organ to produce a multiplicity of special effects.

4. The combination according to claim 1 wherein said digital harmonic pulse generating means comprises a chain of cascaded digital flip flop circuits, the outputs of which are coupled to monostable one shots producing the pulse frequencies.

5. The combination according to claim 1 wherein said digital harmonic pulse generating means comprises a chain of cascaded digital flip flops, the outputs of which are coupled to gating means producing the pulse frequencies.

6. The combination according to claim 1 wherein a number of chains of flip flops of N stages each are connected to each pulse frequency summing means output (and the conventional octave divider chains) and further increasing the master oscillator frequency by a factor of 2N to compensate for the flip flop division ratios thus reducing the undesirable harmonic content of the musical note frequencies appearing at the outputs of said flip flop divider chains.

7. The combination according to claim 1 wherein said master oscillator comprising a crystal oscillator, said high pulse frequency, each connected to flip flop divider chains producing audio frequencies to which other types of musical instruments may be tuned thus allowing a reference for the tuning purposes of other music instruments.

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