US2506723A - Electrical generation of musical tones - Google Patents

Description

y 1950 M. J. LARSEN 2,506,723

ELECTRICAL GENERATION 0F MUSICAL TONES Filed Dec. 31, 1947 2 Sheets-Sheet 1 I50 \6 H \3 t l2 l7 i FIG. I

Sme Wove Source E0 8 Audio Osci. B

FIG 2b FIG. 2a WES i V i E, Eb g Eb 0 Time O Time 50 5H 52 M L Audio Frequency E Amp.

\i 3 5 +B Audio Frequency Osoilioior INVEN TOR. Merwin J. Lursen Aiiv May 9, 1950 M. J. LARSEN ELECTRICAL GENERATION OF MUSICAL TONES Filed Dec. 51, 1947 2 Sheets-Sheet 2 H6 4 wEs H641 v a I E I 1 T/ (E0 V V T E0 E .2' E E 0 .52 I: a:

Tlme- To 22; 74 "7 74 Audio 0- x 0 Amp. Sine Wave S e Wilve Source Source 80 83 d Audio (Oscl Audio 78 Hor9no m'cs Audio 4 Amp 6| All Hormonlcs INVENTOR.

Merwin J. Larsen i atentecl May UNlTED sTATES mes-i arms Mei-win J. Larsen, Villa Park, 111., assignor to Stromberg-Carlson Company, a corporation of New York Application December 31, 1947, Serial No. 795,060

8 Claims. 1

The present invention relates to apparatus for the electrical generation of musical tones and more particularly to improvements in musical instruments of the type employin electrical oscillators of audible frequency for the production of musical notes.

It is well-known that the timbre or tone quality of musical instruments depends upon the harmonic content of the wave form of the musical note produced. Some musical instruments such as the flute, the triangle and the like may produce tones having substantially sinusoidal wave forms. It is also well known that certain musical instruments are characterized by the absence or extreme weakness of certain harmonics and the predominance of others. Some musical instruments, for example, have strong odd harmonics such as the fundamental, third, fifth, etc. and weak even harmonics such as the second, fourth, sixth, etc. Musical instruments of the type often characterized by the term electronic organ, have been constructed so as to be able to imitate the characteristic of various other musical instruments having wave forms of the type referred to above. It is obvious therefore that such musical instruments must be able to produce tones varying from sinusoidal wave forms to those having complex wave forms. Known tone sources for use in electrical musical instruments produce wave forms which are either substantially sinusoidal or else Wave forms which are rich in harmonics. If a. sinusoidal Wave form source only is available, it is necessary subsequently either to distort the sine wave or combine the outputs of various sine Wave generators in order to arrive at a tone of complex wave form. On the other hand, if a complex wave form source only is used, such as relaxation oscillators, or multivibrators, then rather involved filtering is necessary in order to produce tones having a substantially sinusoidal wave form. g

It is apparent therefore that to produce the desired tone quality, it is necessary to have tone sources which are capable of producing audible signals having wave forms varying all the way from asine wave to a wave form of very complex harmonic structure. A plurality of different methods have been employed for accomplishin this result. One method which has been extensively employed comprises employing a plurality of generators for producing only substantially sinusoidal voltages of frequencie following the tempered scale. The complex Wave form tones are then produced by bleeding various harmonics along the tempered scale from those generators whose frequencies exactly or sometimes approximately correspond to the harmonic orders desired and recombining them to produce the desired tones. Another method which has also been extensively used employs means for initially generating tones rich in harmonics and employing suitable filters for getting the desired pure tones Without har monies or the desired combinations of frequencies. A third method starts with sinusoidal voltages and produces complex Wave forms by dis torting techniques. The present invention is partioularly concerned with this third method whereby a simple inexpensive multiple tone source can readily be provided.

It is an object of the present invention to provide a, multiple tone source for a musical instrument which is exceedingly simple and inexpensive and very satisfactory in operation.

It is another object of the present invention to provide a tone source which provides a source of substantially pure tones as well as a source of tones rich in harmonics without the requirement of filtering means or other complicated means for recombining various frequencies to provide complex wave forms.

A still further object of the present invention is to provide a tone source for both pure tones and tones having complex wave forms with simple.

means for providing a vibrato output whenever,

desired.

Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty; which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the present in-l' vention reference may be had to the accompanya ing drawings in which:

Fig. 1 is a schematic circuit diagram to aid in understandin one feature of the present invention;

Figs. 2a, and 2b are curve diagrams to aid in understanding the operation of the circuit of Figs. 4a and 4b are curve diagrams similar to Figs. 2a and 2b to aid in understanding the operation of the multiple tone source of Fig. 3;

Fig. 5 is a circuit diagram similar to Fig. 3

illustrating a modification thereof;

Fig. 6 is a curve diagram to aid in understanding the operation of the multiple tone source of Fig. 5; and

Fig. 7 is a diagram similar to Fig. 5 illustrat- 1 ing still another modification of the present in-- vention.

ence numeral H and the corresponding parts of Fig. 3 are designated by the same reference numerals as in Fig. l. The audio frequency oscillator II is illustrated as a parallel-T type oscillator which is a Specific one of the bridge type of resistance-capacitance oscillators. As illustrated the oscillator H comprises a bridge circuit generally designated at 21 arranged in a so-called parallel-T with one T comprising the serially arranged resistors 22 and 23 and the capacitor 24 connected between the common terminal of the resistors 22 and 23 and ground. The other T circuit comprises the capacitors 25 and 26 connected in series with the common terminal of the capacitors connected to ground through resistors '21 and 2-8, one of which, i. e. resistor 23, is indicated as being adjustable to provide means for obtaining a fine frequency adjustment as for initially tuning the electronic organ. This parallel- T bridge type circuit is disclosed in the Scott Patent 2,173,427 referred to above. The audio frequency oscillator ll further includes an electron discharge valve 30 specifically illustrated as a triode comprising an anode or plate 3!, a cathode 32 and a control electrode or grid 33. The cathode 32 is grounded through a suitable cathode resistor 34 which provides the desired degeneration for improvement of the wave form, while the anode 3| is connected to a source of +B potential 35 through a suitable voltage dropping resistor 36. The bridge circuit 2i described above has one terminal, namely the terminal between the resistor 23 and the capacitor 26, connected to the control electrode 33 while the terminal between the resistor 22 and the capacitor 25 is connected to the plate 35 through a suitable direct current blocking capacitor 38. A suitable resistor is also illustrated as normally connecting the control electrode 33 to ground as indicated at 4|.

In order that a substantially pure sinusoidal potential may be obtained from the audio frequency oscillator N there is provided an output circuit comprising the resistors 42 and 43 connected in series and connected between ground and the plate 3! of the triode 30 preferably through the direct current blocking condenser 38 as illustrated. The sinusoidal output voltage may be obtained at the terminal 44 between the resistors 42 and 43. The resistor 42 preferably provides a very high resistance so as to prevent any frequency change of the oscillator I! when an output potential is obtained as by keying or the like from the terminal 44.

Any suitable means for obtaining a sinusoidal potential from the terminal 44 may be provided. As illustrated the terminal 4% is connected to a suitable movable switch arm 55 adapted to be actuated by a key 41 pivotally mounted at 48. By depressing the finger engaging portion of the key 41 which may comprise the key of an electronic organ the switch 45 is moved into engagement with the stationary contact 69 connected by a suitable conductor to an audio frequency amplifier 5| which in turn has its output connected to a signal reproduction device or loud speaker 52. It will be apparent therefore that the output of the audio frequency oscillator I! may selectively be supplied to the amplifier 5| and loud speaker 52 to produce an audible tone of substantially sinusoidal frequency or in other words a pure tone. It will be understood that in an electronic organ a plurality of oscillators such as I I each capable of producing a difierent frequency will be provided and by suitably keying these oscillators the common conductor 59 ma be selectively connected to one or more of the oscilla various keying circuits of a plurality of oscillators such as l I.

It will be understood that other types of oscillators than the one illustrated may be employed equally well herein, the only requirements being that such an oscillator must have a safe margin of amplitude and a high degree of frequency stability.

By employing the parallel-T type oscillator described above a very desirable arrangement is provided for the injection of a low frequency signal to produce a frequency vibrato. As illustrated in the drawings a suitable key or stop 54 may be provided for controlling a two-position switch 55. Normally the switch 55 engages a contact 55a whereby the control electrode 33 is grounded through the grid resistor 40. Upon actuation of the key or stop, however, the switch 55 is moved into engagement with a normally open contact 55b so as to connect a low impedance low frequency source generally designated at 51 in series with the resistor 43 with one terminal of the generator 51 connected to ground, also designated by the reference numeral 4!. Preferably the generator 51 is a five to eight cycle generator of sufficiently low impedance whereby keying of the switch 55 has no adverse effect. By the proper choice of the resistance value of the resistor 40 the frequency vibrato may be substantially free from amplitude modulation which is very desirable since it permits the gas diode 12 to operate steadily. It will be apparent that a single generator such as 51 may be employed for supplying the vibrato for all of the frequency oscillators such as l l and consequently the conductor 60 connected to the other terminal of the generator 51 and the contact 55b may be common to all of the oscillators such as H.

The gas diode or neon tube I2 is connected in substantially the same manner as in Fig. 1 of the drawings with the resistor [3 connected to the plate circuit of the triode 30. Instead of employing the biasing battery of Fig. 1 of the drawings, however, the terminal |5a connected to one electrode of the diode i2 is connected to the source of +3 potential 35 through the serially arranged resistors 13 and. 36. The source of potential 35 therefore provides the necessary bias for the gas diode l2 whose other electrode is connected to ground as shown. It will be apparent that by suitably adjusting the resistors l3 and 36 any desirable bias may be obtained such as was obtained by varying the voltage of battery [4 in Fig.- 1 of the drawings.

The tone or signal of distorted wave form may also be keyed and, as illustrated in Fig. 3 of the drawings, the terminal 18a between the resistors l1 and I8 is connected to a suitable switch 6| which is controlled by a key 62 pivotally mounted at 63. The switch Bl includes a normally open contact 64 which is connected by a conductor 55' to suitable filters generally designated at 66 the output of which may, if desired, be connected to the audio amplifier 5| for audible reproduction by the loud speaker 52. It will be understood that conductor 65 may be a common circuit for the complex waves produced by the distorting cir-. cuits of other audio oscillators forming a part oi tially suppress the fundamental component/oi Resistor" ti; audit freuuency signatorcdmpi'ex wate form sihcethisiundamental component is avanabieror separatecontrolat theterminal M.- I

In Figs. 4"aand4b'there are illustrated certain wave forms-fonunderstandingthe operationof the distorting circuit of Fig. 3 of the drawings-- which curves are q'uite similar to the curvesshown in Figs.- 2a -and 2b ofthe drawings. The curves E'il'both Figs.- 421" and-4b indicate the sinusoidal Voltage-output of the'audiooscillator II, it' beingobserved that a larger voltage is-p'resent'in the curve of Fig. 4b which is obtained by increasing thepotential of the $13 source 35 1 as by adjusting'theresistor 36: Thecurve's Ea of Figs; 4a and 1 46 representthe potentialsat the terminal [512' oi tl ie 'dioder2 which potential is displaced from alsdbeing of-greater magnitude in Fig; 415

tHan=ih-'F*i .'-4aa v It'wiil 'be" understood thatvarious circuit arrangements and various circuit constants may be" employed 4 in" connection with" the ai -range: nie'nt ofFigz' 30f the drawings-for example. In order, however; to illustrate the relative magnitildes of-the principal elements of a typical aircuilf arrangement which" has been found to satis= factorily' embody the present invention the" fol-' lowing approximate values of suchelern'ents" to gether" with other" pertinent information" are gi iien foraparticular'devicei It shouldbe under stoodtl iat these values are given byway of exaniple onl yaiidfno't by Way of limitation.

Gas'diodewa NE 9 /1; watt) Resistor-l3; 4:7 mego'hms Capacitor l6: has-such a value cf capac reactance at the 'oscii la-toi frequency is 2.2

megohms; Resistor l1 .2 mego'h'ms" Resistor-l8" Gilmegohm' Resistor? 0.27 megohin'" 0.27- megohm- Resistor 2e I r capacitance in' micrefar= capacitor 52 4;

adsapproximately equal" to 118/ wheref i's'the frequency; in cycles Capacitor- 25: the capacitance 'o'fcapacitor "2e CEDRCWOFZE V2 the capacitance of ca;-

paeitor' 24 18,000 ohms Oto l'OgOOO ohms Resistor 28' H Electron discharge itan'cethat its capacitive" ssm of the csmt'c' be iiiritio rieu-"abeyef certaifi in'str-unfen notably the woodwindssuch as the clarinet, have strong odd harmctiicsand weak even fharmoni' With the'tcne source illustratedfinFiQ 3 of'th drawings it; is necessary: to do a: 'al' amount of filtering to eliminate the evenhe monies; InFig 5"of" the drawings there is illusf trate'da niodification of thepresent invention in which there is essentially provided am netorfesource which comprises a sine wavej tone' sourcea compleii wave tone sourcein which sub? stantially only odd 'harmonics" are present; and a complex, wave form sourr'seinwhich 'substan ti'aliy all harmonics; are present. The'cor're' same reference numerals-as in the preceding figures. It will be understood that the wave'Ee such as is shevvninFig. ib; fer example, could notbe use'dtoproduoe cl a net tone which containssubstantia'lly oniy odd harmonics, without "resorting to cumbersome filtering. ever, the Wave Ea of Fig. 4b, for example, were" distorted so both thepositive and negative halves were'alike the resulting wave would contain sub- 5 stantiallyonly odd harmonics; This is accomplished by the" circuit arrangement of' Fig. 5' where two gasl'diodesare' employed, designated as lZ'aandiZb respectively; The diodes are conheated in series"with the c'oirinion terminal i0" 30 corresponding to "thete'rminal i5ain' the preceding" figures ofth'e drawings. The other terminal of the diode- :aa is connected to the'source 3'5.

of'+B potential through a suitable potentiometer" comprising" the resistor I! and the adjustable tapiZ. Thefotherterininal'of the gasdiode i211 is'groun'ded through a suitable resistor i3, The

potential ofthe' +B source'35 mustbesufliciently large tofire both diodes lid and 52b alternately. Theiterminal Tilis connected tolthe sine wave in source Ii through the current limiting resistor is and the blocking, capacitor it. The terminal lilis also connected to ground through serially arranged blocking capacitor 'i't'fandresistorslii andfl'ir The resistors lfiland H are illustratedasliaving a co'mm'on' terminal 38 which provides a' source of potential of complex wave forrn' containing substantially only odd harmonics. By virtueof'tliec'apac'itors Hi and lfi' the common.

terminal HTo'fthe gas diodesliz'a and?! 2b main- ,v talifed at anzaverage direct current petentiai between ground and the positive potential 'ofthe source" 35 whereupon a very. symmetrical wave form is obtained.

Iii .Fig, 6 ofithe drawingsthere is illustrated by the curve Ea the complex wave form obtain-- ablewhich 1 contains substantially only odd harmonics. The oscillator sine wave voltage Eeis also. shown.

The potenti al obtainable at-theterminal18 m maybe' supplied th'rough a suitabie switch 8Q actuated by a key 86 .pivotally meunted at 82:

Switch 85 illustrated. as being engageable' with a normally open contaetfit connected by means: of afsuit'able conductor 3% to suitable filters and g subsequently tothe: audio amplifier. With the arrangement disclosed-in Fig. 5 of the'drawings a-very simple way --of obtaining a pure-sinewave; ,1- a wave rich in all harmonics, and a Wave richin'odd harmonics only is provided. The three diff-- ferent wave forms are illustratedschematically in "Fig? Sadjacent' the conductor wherein.

particular wave form appears.

ltshouid "be understood that instead of gas... diodes IZ'aand [2b ordinary clio'desmight equally] well be employed-and inFig. 7"o'f' the drawings" spending parts o'fF'ig; 5 are designated by the If, how

the

the identical circuit of Fig. with the tubes 52a and I222 replaced by ordinary diodes designated by the reference numerals iii) and 9! respectively, is shown. As illustrated the anode of the diode 9B is connected to the terminal it) while the oathode of the diode ii is connected to the terminal 10. It will be understood that when the potentiometer comprising the resistor H and the variable tap 12 is employed the odd harmonic output can readily be controlled merely by changing the common bias. With this arrangement it is possible to tie keys 62 and 8t together or in other words eliminate one of the keys thereby making possible a keying system employing a minimum number of cantacts and yet retaining a degree of quality control;

In view of the detailed description included above the operation of the multiple-tone source arrangements described will be apparent to those skilled in the art and no further discussion thereof is included herewith.

While there have been described and illustrated what are at present considered to be the preferred embodiments of the presentinvention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the present invention. It is aimed in the appended claims to cover all such changes and modifications as fall withinthe true spirit and scope of the present invention.

What is desired to be secured by Letters Patent of the United States is:

1. In a musical instrument, an oscillation generator for developing an audible signal having a substantially sinusoidal wave form, means for developing a signal of adiustably complex wave form comprising a distorting circuit including a gas diode characterized by having a firing potential which is substantially higher than the potential for sustaining current flow through said d ode, means for impressing the output of said oscillation generator across said diode, the variation in potential of the output of said oscillation generator exceeding the difference in Voltage across said diode for firing said diode and for susta ning current flow therethrough, and means for applying a direct current bias across said diode, the value of said bias determining the wave form of said developed signal.

2. In a musical instrument, an oscillation generator for developing an audible signal having a substant ally sinusoidal wave form, means for developing a signal of adiustably complex wave form comprising a distorting circuit including a gas diode characterized by having a firing potential which is substantially higher than the po tent al for sustaining current flow through said diode, means for impressing the output of said oscillation generator across said diode, the variation in potential of the output of said oscillation generator exceeding the difierence in voltage across said diode for firing said diode and for sustaining current flow therethrough, means for applying a direct current bias across said diode, the value of said bias determining the wave form of said developed signal, and means for obtaining a potential of said determined complex wave form from across said diode.

3. In a musical instrument, an oscillation generator for developing an audible signal having a substantially sinusoidal wave form, means for developing a signal of adjustably complex wave form comprising a distorting circuit including a gas diode characterized by having a firing potential which is substantially higher than the potential for sustaining current flow through said diode, means for impressing the output of said oscillation generator across said diode, the variation in potential of the output of said oscillation generator exceeding the difference in voltage across said diode for firing said diode and for sustaining current flow therethrough, and for applying an adjustable direct current bias across said diode, the value of said bias determining the waveform of said developed signal, and means comprising a serially arranged capacitor and resistor connected across said diode whereby a potential of said determined complex wave form may be obtained across said resistor.

i. In adevice for producing musical tones including tones of sinusoidal wave form and tones of adjustably complex wave form, the combination of a source of alternating potential of audio frequency having a substantially sinusoidal wave form; means for distorting said potential of audio frequency comprising an electron discharge valve of the type requiring a substantially greater potential across its terminals to initiate ionization than to maintain ionization once such ionization has occurred, the sinusoidal wave form output of said source having a variation in potential exceeding the difference in potential across said valve between that existing at the instant of ionization and that for maintaining ionization; means for connecting said valve across said source; and means for impressing a direct current potential across said valve of suflicient magnitude so that the sum of said audio frequency potential of sinusoidal wave form and said direct current potential equals the ionization potential of said valve at some point during each cycle of said audio frequency potential whereby the potential across said valve comprises an audio frequency potential rich in harmonics, the magnitude of said direct current potential determining the wave form of said developed audio frequency potential.

5. In a device for producing musical tones including tones of sinusoidal wave form and tones of adjustably complex wave form, the combina-- tion of a source of alternating potential of audio frequency having a substantially sinusoidal wave form; means for distorting said potential of audio frequency comprising a gas diode of the type requiring a substantially greater potential across its terminals to initiate ionization than to maintain ionization once such ionization has occurred, the sinusoidal wave form output of such source having a variation in potential exceeding the difference in potential across said diode between that existing at the instant of ionization and that for maintaining ionization; means for connecting said diode across said source; and means for impressing a direct current potential across said diode of sufficient mag nitude so that the sum of said audio frequency potential of sinusoidal wave form said direct current potential equals the ionization potential of said valve at some point during each cycle of said audio frequency potential whereby the potential across said valve comprises an audio frequency potential rich in harmonics, the magnitude of said direct current potential determining the wave form of said developed audio frequency potential; and a circuit associated with said diode for providing a. means of extracting a potential having a wave form rich in harmonics.

6. In a musical instrument, a resistance-caamoares pacitance oscillator capable of producing a potential of sinusoidalwave form comprising an -eleetron discharge valve including at least three ---e'lec'trodes one of which is a control electrode, --a-=parallel-T network connectedacross *two of saidelectrodes, a resistor -connected between said "control electrode and ground, means'for producing a frequency vibrato comprising a low "frequency low impedance sourceconnected inseries -w-ith said --resistor, and a distorting circuit -compr-'ising'a gas diode --connected 'tosaid oscillator for" providing a source of 'poten'tialo'f" audiofrequency and of --complex wave form.

" '7." Ina musical instrument, an oscillation gen- "orator-for developing a firstaudible signalhav- *inga substantially sinusoidal wave form, means "for developing two additional signals of complex 'wave form'one containing %both odd and even harmonics and the other containing. substantially only odd harmonics, comprising 'a distorting-ma 'cuit including a pair-o'fgasdiodeseaeh character-- ized by having a Thing potential which is subs'tantially-higher'than-thepotential for sustaining "current fiow therethrough, means for connecting one terminal oi'each-o'fsaid diodesto-a common terminal, means for-connec'ting the other terminal of one of said diodes to a sourceof direct current potential, means for connecting' the other "terminal of said other diode to ground, means "for" connecting said oscillation generator across said other diode, the variation impotentialof the output '0f 'S&id oscillation generator exceeding 'the dilference in voltage :at said common term'ina l "required for firing each'of said diodea aoircuit connected to said comm-on terininalior supplying 5 :apotential of complex wave "form containing-suite stantially only odd harmonies, and means con- 'nected to said otherterminalof said otherdiode for supplying a potential o'i? complex waveform rich in both odd and even harmonics.

' 8. 'In a musical 'instrument'an oscillation-generator for developing a "first audible s'ignal' ha ving a substantially sinusoidal :wave'=form,wimeans for' developing two-additional signals of complex wave form one containing both odd and even harmonics and the other containing only odd harmonics comprising a distorting circuitinc'lud- .ingia pair of 'diodeseach characterized by having :a firing potential which is substantially higher than the potential for sustaining current flow therethrough, means for connecting thezanode of :one "diOd :and the cathode of the other -.-diode to a common terminal, means for connecting-the cathode ofsaid one diode to a source of adjustable direct "current potential, means gior connecting the anode of said other diode to ground, means for connecting :said oscillation generator-across ".said otherdiode, the variationi'in" potential. of ithe output of said oscillation generator exceeding the :difierence 61in -voltage at "said common terminal xrequired"iorifiringneach of said diodea a circuit ..:connecte,drto :said common terminal i or "supply-- ing'ra potential. of complex wave form containing substantially only odd harmonics, ,eznd cmeans connected to the anode :ofzsaid other diodefor supplying 'a :potential of comrilexwave "ai orm irioh in both :odd-andeven harmonics.

MER-WIN J.

*REFERENGES GIT-ED The followingreferences are of record tin tiie ifile of :patent:

UNITED STATES PATENTS

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