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THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA VOLUME 27, NUMBER 3 MAX7, 1955•

Electronic Synthesizer

HARRY F. OLSON AND HERBERT BELAR RCA Laboratories,Princeton, New (ReceivedJanuary 15, 1955)

The electronicmusic synthesizer is a machinethat producesmusic from a codedrecord. The codedrecord isproduced by a musician,musical engineer, or composer with a fundamentalunderstanding of the composi- tionof .The electronicmusic synthesizer provides means for theproduction of a tonewith anyfre- quency,intensity, growth, duration, decay, portamento, , , and variation. If theseproperties of a toneare specified, the tone can be completely described. The advantage of theelectronic music synthe- sizeris that it canproduce new and radicaltone complexes for musicalsatisfaction and gratification.The newsystem does not displacethe artist and musician of today.It doesnot takethe placeof talentcombined withwork. The electronicmusic synthesizer provides the musician,musical engineer, and composer with a new musicaltool with no inherentphysical limitations.

INTRODUCTION for the productionof musicalsounds opens an entirely USICis the art of producing pleasing, expressive, new field for the production of recordedmusic. For or intelligiblecombinations of tones.The example,there is the possibilityof entirely new tone of original music are producedby the human voice or complexesand combinationswhich cannot be achieved by an instrumentactuated by a musician.Most music in conventionalinstruments. Furthermore, in the case is recordedand translatedinto soundsby meansof a of conventionalinstruments, the musicianis limited to symbolicnotation on paper. The ultimate objective the useof tenfingers, two hands, two feet, and the lips, destination of all musical sounds is the human ear. eitherseparately or in variouscombinations, to perform Thus the productionof musicconsists of the following the different operations. This limitation does not processes'The symbolicnotation upon paper by the exist in the synthesizer. Conventional instruments composer,the translationof the symbolicnotation into producevarious noises such as the rushingof wind in musicalsounds by the musician,employing either his wind instruments,bow scratchin the viol family, own voice or a or both, and the various clatters and rattles in plucked and struck actuation of the human hearing mechanismby the string instruments,and mechanismrattle in any musical sounds. instrumentin which keys, valves, levers,and shafts are used. These undesirable noises do not exist in the The physicalproperties of a sound are frequency, intensity, wave form, and time. The psychological electronicmusic synthesizer.With the advent of the characteristicsof a sound which depend upon the electronicmethod for the productionof musicaltones, physical propertiesare pitch, loudness,timbre, and new musical compositionscan be written which take time. Every sound in nature may be describedin advantageof the superiorcharacteristics of the elec- terms of these attributes of a sound or tone. tronic musicsynthesizer. It is the purposeof thispaper to describean electronic Oncea soundor a tone has been describedby means of the above characteristics,it is possibleto generate music synthesizercapable of producingany pre- determinedmusical tone and any combinationof series or producethis tone by electronicmeans. Thus it will be seenthat it is possibleto generateany tone produced of musicaltones combined with a systemfor translating the symbolicnotations of a musicalcomposition into by a voice or a musicalinstrument by employingan the correspondingtones and means for recordingthese electronicsystem. In addition,it is possibleto produce soundson a phonographrecord. musicaltones which cannot be producedby the voiceor conventionalinstruments. In other words,the process PHYSICAL CHARACTERISTICS OF MUSIC • of translatingthe musicalnotation on paper into the correspondingmusical sounds can be accomplishedby The medium of transmission from the musician and an electronic system. Furthermore, the electronic musical instrument to the listener is sound waves. A systemcan reproduceor createany soundor combina- toneis a soundwave capable of excitingan auditory tions of sounds,which have or have not been produced, sensationhaving pitch. The propertiesof a musical that may have any possible musical significance. tone are frequency,intensity, wave form, and time. The electronicsystem for the productionof musical It is moreconvenient to describethe propertiesof a soundshas been termed an electronicmusic synthesizer. tonein termsof frequency,intensity, growth, duration, One of the usesfor an electronicmusic synthesizer is decay,portamento, timbre, vibrato, and deviations.If for the productionof phonographrecords. Of course, theseproperties or a toneare completelyspecified, the the phonographrecords thus producedcan be played • H. F. Olson,Musical Engineering(McGraw-Hill Book Com- in the conventionalmanner. The use of a synthesizer pany, Inc., New York, 1952). 595

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Loudnessof a soundis the psychologicalcounterpart FREQUENCY (PITCH) of intensity. Loudnessis the intensity attribute of an IOOO ioooo FREQUENCY IN CYCLES PER SECOND auditory sensation,in terms of which sound may be orderedon a scaleextending from softto loud.Loudness. 120•--- dependsprimarily upon the intensity of the stimulus, but it alsodepends upon the frequencyand wave form INTENSITY _•SOl- ! (LOUD NESS) of the stimulus. In order to take full advantage of the intensity

o range of the human hearingmechanism, the electronic Ir• DURATION musicsynthesizer should cover a volume range of 0 to GROWTH 120decibels (Fig. 1). In general,the lower20 decibelsof STEADY STATE DECAY this range is of little practical significancebecause DURATION sounds in this intensity range are masked by the TIME IN SECONDS ambient noise level which exists in all conventional living rooms,halls, and theaters.

PORTAM ENTO Duration

TIME IN SECONDS Duration is the length of time that a note persistsor lastswithout interruptionor discontinuityin the sound output (Fig. 1). From the standpointof the duration TIMBRE of a tone, musical instrumentsmay be classifiedas ,oo ,ooo ;&DO follows: fixed duration, variable but fixed maximum FREQUENCY IN CYGLES PER SECOND duration, and unlimited duration. The electronicmusic synthesizershould be capable VIBRATO vl/v VVVV of producingall thesevariations of the duration of a tone. AMP LITUDE FR E Q UENCY MODULATION Growth and Decay Fro. 1. Properties of a tone. The growth of a tone involvesthe time requiredfor the soundto build up to somefraction of the ultimate tone can be completelydescribed. The electronicmusic value (Fig. !). The decayof a toneinvolves the required synthesizerdescribed in this paperis basedupon the timefor the sound to fall to'somefraction of theoriginal breakdown of a tone into these characteristics. There- intensity (Fig. 1). Most of the growth and decay fore, it appearsappropriate at this point to definethe characteristicsof musicalinstruments are exponential propertiesof a musicaltone. functions. The electronicmusic synthesizershould be capable Frequency--Pitch of producingany desirablegrowth or decay charac- Frequencyof a soundwave is the numberof cycles teristic. The electronicsynthesizer is not limited to an occurringper unit of time. exponential function but can produce almost any Pitch of a soundwave is the psychologicalcounter- type of growthand decaycharacteristic. For example, it appearsthat linear growthand decaycharacteristics part of frequency.The pitchof a soundis that attribute are more pleasingin somecases than the exponential of auditorysensation in termsof whichsound may be type. This can be achievedby electronicmeans but orderedon a scaleextending from low to high, suchas not by a natural vibrating system. a musical scale. Pitch dependsprimarily upon the frequencyof the soundstimulus, but it alsodepends Frequency Glide--Portamento uponthe sound pressure and wave form of thestimulus. In order to take full advantageof the frequencyrange Portamentois a specialcase of frequency,growth, and of the human hearing mechanism, the electronic decayin whichthe passagefrom a toneof onefrequency to a tone of another frequency takes place in a con- synthesizershould cover the entireaudible frequency tinuous glide through all the interveningfrequencies. rangeof 30 to 15000 cycles as shown in Fig. 1. The electronicmusic synthesizer should be capableof glidingfrom one frequencyto anotherfrequency. Intensity--Loudness Wave Form--Timbre The soundintensity in a soundfield in a specified directionat a point is the soundenergy transmitted A complexsound wave or tone is made up of the per unit of timein a specifieddirection through a unit fundamentalfrequency and overtones.The timbre of a area normal to this directionat the point. tone is expressedin the number,intensity, and phase

Downloaded 19 Feb 2013 to 160.39.22.56. Redistribution subject to ASA license or copyright; see http://asadl.org/terms ELECTRONI C MUSI C SYNTHESIZER 597 relationsof the components,that is, the fundamental must be providedin the synthesizerto obtain a devia- and overtones.Timbre then may be said to be the tion from the regularwhen this is desired.Of course, instantaneouscross section of the tone. For practical there are many instanceswhere the performercannot considerationstimbre is the tonalspectrum. A spectrum obtain the required mechanical quality which is graphis shownin Fig. 1. The relativeamplitudes of the desired.In thesecases, the synthesizeris, of course,far componentsof the resultant tone are depicted as a superior.It can also be superiorfor the caseswhere function of the frequency.The heightsof the vertical random effectsare desired,because the results can be lines are proportionalto the amplitudesof the funda- made even more random than is possibleby human mental and the overtones.The position along the means,as for example,by the useof the random nature abscissadetermines the frequency. of thermal noise to control the random effects. The electronicmusic synthesizershould be capable of producinga tone of any spectrumtogether with SYNTHESIZER REQUIREMENTS meansfor changingthis spectrumduring the sounding From the precedingsection it is evident that in of the tone. order to synthesizeany musical tone whatsoever,the synthesizer must provide the following facilities. Low---Vibrato Means for producing a tone with any fundamental frequencywithin the audio-frequencyrange; means for Vibrato is a term to designateprimarily a frequency producinga tone with any overtonestructure; means modulationof a musicaltone (Fig. 1). The vibrato is for producinga tone of any growth,duration, or decay accompaniedby an amplitude modulation (Fig. 1). characteristic; means for changing the overtone In somecases the frequencyand amplitudemodulation structureat any time; meansfor introducinga vibrato; is accompaniedby a variation in the timbre at the meansfor changingthe intensity of the tone; meansfor modulation frequency. The vibrato is used as an providing a portamento or glide from a tone of one artistic embellishmentin the voice and in a large num k• • in•f•,,,•o•f• In rreneral the modulation frequencyto a tone of a differentfrequency; means for providinga deviationfrom the regular.It is the purpose frequencyis sevencycles. of the section which follows to describe an electronic The electronicmusic synthesizershould be capable musicsynthesizer satisfying the aboverequirements. of producingeither or both amplitude or frequency A schematicblock diagram of an electronicmusic syn- modulation of any desired frequencyas well as a variation in the timbre. thesizerwith meansfor producingall the characteristics of a musicaltone outlined above is shownin Fig. 2. The coded paper record controlsall the functionsof Irregular Deviation the electronicmusic synthesizer. The output of the syn- One of the beautiful and artistic characteristics of thesizeris recordedon a disk record.The codedpaper sometypes of musicis the lack of a mechanicalquality record and the phonographrecorder are driven in of the rendition.Unless specific steps are taken in the synchronismby an interconnecting cable drive. In rendition of somemusical selections by meansof the the completeelectronic music synthesizer two complete electronicmusic synthesizer,the result will be too channels,as shown in Fig. 2, are used and operated regular and, therefore, inartistic. Therefore, means from the single coded paper record. This makes it

CHANNEL I 'YAND H LP' I•J VOLUMEIJ FREQUENCY H RE$ON&TORH TIMBRE• II IIco.,,o i i

TURNTABL , "

DRIVING CABLE

CODED PAPER RECORD

CHANNEL 2

FIG. 2. Schematicdiagram of the electronicmusic synthesizer.

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TUNING FORK UNIT

I I SN' I I Fro. 3. Circuit diagram I I of the combination tuning fork and . OUTPUT

+B possiblefor the coded paper record to set up one to the motion.The input and output coilsof the tuning channel while the other channel is in operation and fork are electronically coupled to a producinga tone. Furthermore,one channelcan start system to provide the resonant element of the oscil- playing a tone beforethe other channelstops playing lating system.The tuningfork is housedin an evacuated a tone. Everything is duplicatedin the secondchannel chamberto reducethe dampingeffects which would be exceptthe twelve tuning fork oscillatorswhich supply introduced by surroundingair. The twelve tuning the tonesin oneoctave. It is the purposeof the sections forkscover the octavefrom Fs• to F6.The frequencies which follow to describe the elements of the electronic in this octavefor the equally temperedscale are shown musicsynthesizer shown in Fig. 2. in Table I. FREQUENCY SOURCE In order to reduce the number of contactsrequired to selectthe proper frequencyin an octave, a binary The first requirementin a synthesizeris the genera- codingsystem is usedas shownin Fig. 4. This binary tion of the fundamental frequency.The fundamental codingemploys a relay tree which makes it possible frequency sourcein the electronicmusic synthesizer to selectany one of the twelve frequenciesby means consistsof twelve electricallydriven tuning forks with of four circuits in the master control system. The frequenciescorresponding to an octave in the equally temperedscale. The useof an electricallydriven tuning code for the frequenciesin this octave is shown in Table II. fork makes it possibleto maintain the fundamental frequencyto an accuracyof better than onepart in ten thousandor one-eighthof a cent, a cent being one twelve-hundredth of an octave. A schematic circuit diagram of the combination RELAY TREE tuning fork and electronicoscillator is shownin Fig. 3. The tuning fork suppliesthe highly resonantsystem in the combination mechanical and electronic oscillator. The tuning fork is set into vibration by the forces generatedby the magneticfield of the currentcarrying

I coil acting upon one of the tines. The motion of the OUTPUT other tine varies the flux linking the other coil and I therebyinduces a voltagein the coil which corresponds o ,• I I I '" I • I TA]•.E I. The frequenciesof the octave covered by the twelve tuning fork oscillators. I I I •I I I Note Frequency • I , f I _El F6 i-- Gat, 739.989 Ga 783.991 A at, 830.609 a 880.000 Bah 932.328 Ba 987.767 Co 1046.502 DoE, 1108.731 ,,.,.,B•.,•_._.• PAPERRECORD Do 1174.659 E•b 1244.508 E0 1318.510 ,•-•---DRUM F0 1396.913 Fro. 4. Schematicdiagram of the frequency selecting systemfor one octave.

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TABLE II. The code for selecting any frequency in an octave.

Note Frequency Code

F•g G•b 739.989 2 G• 783.991 10 G• A •b 830.609 6 A • 880.000 14 A•g B•b 932.328 1 B5 987.767 9 C6 1046.502 5 Crg D•b 1108.731 13 D• 1174.659 3 D•g, E• 1244.508 11 E6 1318.510 7 F• 1396.913 15 Noise All 12

The storagesystem in the electronicmusic synthe- sizeris a punchedpaper tape record15 inchesin width. The punched paper record stores all the information Fro. 5. Photographof the punchedpaper record,the keyboard punches,the brushes,and the paper drive mechanism. on frequency, growth and decay, duration, volume, timbre,vibrato, portamento,and deviations.See Fig. 5. The two edgesof the paper are providedwith sprocket amplified by a conventional three-stage resistance- holeswhich engage teeth in the metal drivingdrum and coupledamplifier. The frequencyoutput of the noise thereby insuresa positive drive of the paper record. is random with a power distribution per The drum is driven by the turntable motor so that cyclewhich is independentof the frequency. the drum and turntable move in synchronism.The OCTAVE SELECTOR holes in the paper are punchedby means of the - board system shown in Fig. 5. The brushes make The tuning fork oscillator covers fundamental contact with the drum through holespunched in the frequenciesin an octaveof the equally temperedscale. paper at appropriate locations. The paper may be Frequencydividers and multipliers are used to cover moved at a speedof from 2 to 8 inchesper second.A the fundamentalfrequencies of the equally tempered detailed descriptionof the codedpaper recordwill be scalein the frequencyrange from F0• to Fs, that is, given in a later sectionof this paper. 23.124 cyclesto 5587.65cycles. A schematicdiagram In addition to the twelve frequenciesin the equally showingthe frequency dividers and multipliers and temperedscale, it is possibleto employthree additional the octave selectingsystem is shownin Fig. 7. This sound sources in the four circuits in the master control systemis termedthe octaver.Any of the eight octaves system as shown in Fig. 4. One of these sourcesis a can be selectedby meansof three circuitsin the master random noise source. control system.The codefor selectingany one of the Random noiseis usefulas an addition in simulating seven octaves from F0• to F8 is shown in Table III. such instruments as drums, maracas, tambourines, Schematicdiagrams of the frequencymultipliers and string and wind instruments.When used with are shownin Figs. 8 and 9. The incomingsine wave passfilters with a narrow frequencypass band, supplied by the tuning fork oscillatorsis converted the noise sourcecan be used to produce weird and into a rectangularwave having the samefundamental unusual sounds.A schematiccircuit diagram of the frequency as the input by the first two random noise sourceis shown in Fig. 6. The source vacuumtubes. The next two tubesconvert the square of noise is hot cathode triode gas tube. The supply wave into a saw tooth wave. A saw tooth wave contains voltage to the noiseis kept at a constantvalue by the all the harmonicsof the fundamental.The spectrum cold cathodegas tube. The output of the noisetube is showingratios of amplitudesof the harmonicsto the

•B

0 • 6F6 FIG. 6. Circuit diagram of the random noise source.

OUTPUT

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TA•.•. III. The code for selecting any one of seven octaves. RELAY TREE Octave Code INPUT o F0• to F• 5 F• to F•. 1 F•.• to Fa 6 Fa• to F4 2 F4• to F5 4 Fs• to F6 0 F6• to F7 3 FT• to F8 7 I OUTPUT I o

FREQUENCY DIVIDERS

I I I I SHAPERS

SHAPERS

FREQUENCY BRUSHES BRUSHE••.••••PAPErRECORD MULTIPLIERS SHAF•RS ß -•--DRUM Fro. 7. Schematic diagram of the frequency dividers and Fro. 8. Schematicdiagram of the frequency multipliersand the octave selectingsystem. dividersand multipliers. amplitude of the fundamental for a fundamental range from F0• to F8 containsthe fundamentaland frequencyof 440 cyclesfor a saw tooth wave is shown all the harmonics with the ratios shown in Fig. 10. in Fig. 10. Thus it will be seenthat each tone in the By meansof the frequencydiscriminating systems to be

6SN71

i•P,

•1 6SN?

Fro. 9. Schematiccircuit diagramof the frequencymultipliers and dividers.

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GROWTH, DECAY, AND DURATION CONTROL The time required for a tone to build up to some O , fraction of its ultimate value varies over a wide range in different musical instruments. For example, in the m -I0 plucked and struck string instrumentsand practically all types of percussioninstruments the buildup time is m .-20 relatively short. On the other hand, the buildup time of an organ pipe is relatively long. The time required ß -$0 ..... for a tone to fall to somefraction of its originalintensity varies over a wide range in different musical instru- ments. The growth and decay characteristicsof a tone '4010E P' 4 8 I0$ P' 4 8 I04 influencesthe character of a tone to a very marked R,•,,.•._Q_•ENCYIN CYCLES PER SECOND degree.In practically all conventionalmusical instru- Fro. 10. Spectrumof a having a fundamental ments the growth and decay characteristicsare ex- frequencyof 440 cycles. ponentialfunctions. For example, in the growth of a tone, the sound describedin a later section,it is possibleto obtain pressurep, in dynes per square centimeter, produced practicallyany overtone structure in any toneproduced by a musicalinstrument is given by by the electronicmusic synthesizer. The combinationof the systemshown in Figs.4 and p=p0(1- e-kt), 7 makesit possibleto selectany frequencyfrom F0• wherep0 is the ultimate or steady-statesound pressure, to Fs, a total of ninety-sixseparate frequencies by means of seven circuits or seven brushes and seven in dynes per square centimeter, k is the constant of the instrument, and t is the time in seconds.In the rows of holes in the paper record. This showsthe decay of a tone, the sound pressurep, in dynes per advantageof a binary codingsystem in reducingthe squarecentimeter, produced by a musicalinstrument numberof rowsof punchedholes required in the paper is given by record.For example,in the eighty-eightnote player p=Poe-kt, ,eighty-eight rows of holesin the paperrecord are used to select the frequency. where po is the soundpressure, in dynes per square

o

OUTPUT

o

+B

-105

J- 8RUSHIS• • •/ RELAYS

o DRUM

Fro. 11. Schematicdiagram oœ the electronicsystem for producingthe growthand decayof a tone.

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system.In addition,different values of the growthand decay can be preset in the electrical circuits. The z o growth and decay is accomplishedby varying the amplificationof the push-pulloutput stage by changing TIME IN SECONDS B TIME IN SECONDS the dc bias applied to the grid of the control tubes. The voltagebias applied to the gridsduring the growth steadystate and decayperiods is obtainedthrough the application of a network consistingof vacuum tube rectifiers,resistors, and capacitors.A few of the typical

C TIME IN SECONDS D TIME IN SECONDS growthand decaypatterns obtainable with this system are shownin Fig. 12.. Fro. 12 Typical growthand decaypatterns obtainable The graph A of Fig. 12 depictsa growthand decay with the systemof Fig. 11. characteristicdescribed by exponentialfunctions. The growth and decayare moderatewith respectto time. centimeter for t-0. In an electronic system it is The graph B of Fig. 12 depictsa very rapid growth possibleto obtain growth and decay characteristicscharacteristic. The decaycharacteristic is an exponential whichare exponentialfunctions as well as all mannerof functionwith a suddendecrease in the decayrate during other functions.This it will be seenthat the possibility the decay period. The graph C of Fig. 12 depicts of new typesof growthand decaycharacteristics in an discretechanges in both the growthand decaycharac- electronicmusic synthesizer opens a new vista of tone teristics during the growth and decay cycles. The possibilities.A schematicdiagram of the electronic graph D of Fig. 12 depictsrelatively long growthand decay characteristics. The growth, duration,and decaysystem performs a AMPLIFIER RATOR GENERATORAMPLIFIER doublefunction, namely, it opensand closesthe synthe- sizer channel and controls the growth, duration, and DC DC decay.That is, all the elementsof a synthesizerchannel I FIL are establishedbefore the system is unblockedby the growth system. FIG. 13. Schematicdiagram depictingthe elementsof the frequencyglide follower. FREQUENCY GLIDER growth, durationand decay systemused in the elec- Portamentois a continuousglide in frequencyfrom tronic music synthesizeris shownin Fig. 11. Eight a tone of one frequency to a tone of a different fre- different growth and decay characteristicscan be quency. A portamento can be executedby voice, obtained from three circuits in the master control ,, and other instrumentsof the variable

6SH7 884 6H6 6H6 884

V•105 T ? VRI05

II TOHEATERS 115A• o i ', Fro. 14. Schematiccircuit diagram of the frequencyglide follower.

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to anotherfrequency is shownby the blockdiagram of Fig. 13. A circuit diagram of the frequencyglide followeris shownin Fig. 14. The incomingsignal is amplifiedand convertedinto a seriesof negativepulses. The pulsesare sent through an integrator and a low A TIME IN SECONDS passfilter. The resultantdirect current is amplified and fed to an oscillatorin which the frequencyis a functionof the direct currentinput. The output is fed to an amplifierand pulsegenerator. The output of the pulsegenerator is oppositeto that of the pulseof the incomingsignal. The systemis a comparisonsystem in which the frequencyof the oscillatoradjusts itself to TIME IN SECONDS FIG. 15. Typical fre- quency glides obtain- the input frequency.If the input frequencychanges able from the system of from onefrequency to anotherdifferent frequency in a Figs. 13 and 14. discontinuousstep, the directcurrent oscillator changes from this frequencyto the new frequencyin a con- tinuous manner. The comparisonsystem can be adjustedso that the glide is accomplishedin a smooth C TIME IN SECONDS transition or in a seriesof approximationsby the amountof amplific.ation betweenthe oscillatorand the secondpulse generator. The glide systemwill executea singletype of glide without any outsidecontrol. However, if it is desiredto have the glide changein any part of a musicalselection beingsynthesized, the changesare controlledby means D TIME IN SECONDS of a relay tree actuatedby contactsand a row of holes not usedfor other purposes. pitch type. In one type of portamentothe frequency A few typicalfrequency glides which may be obtained transitionoccurs in a singlesmooth glide. In another by meansof the systemshown in Figs. 13 and 14 are type of glide, the secondfrequency is approachedin a shownin Fig. 15. The frequencyglide of Fig. 15A seriesof successiveapproximations. depictsa relatively rapid and smoothtransition from The systemfor obtaininga glide from onefrequency one frequencyto anotherfrequency. The frequency

6BE6

I I

OUTPUT

I ••j o i I I I i I INPUT I I o I 6BE6

t "]'- +• I !

! I I • I ! ! I I I I I I I

RELAYS

DRUM

16. Schematicdiagram of the electronicsystem for controllongthe volume of a tone.

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LOW PASS FILTERS HIGH PASS FILTERS -I

TIME IN SECONDS

TIME IN SECONDS

Fro. 17. Typical volumechange characteristics obtainable with the systemof Fig. 16. glide of Fig. 15B depictsa relatively slow and smooth transition from one frequency to another frequency. IN The frequencyglides of Fig. 15C and D showthat the • OUT secondfrequency is approachedby a seriesof approxi- 0 mations. All of the frequencyglides shown in Fig. 15 Fro. 19. Variable high and low passfilter system. can be executedby the voice or by musiciansusing conventionalinstruments. The type of frequencyglide in the musicsynthesizer. In addition,the volumeof a dependsupon the particular effect that is desired to tone may be changedduring the soundingof the tone. obtain the proper artistic effects. A few of the typical volume changesthat may be VOLUME CONTROL obtainedby meansof the systemshown in Fig. 16 are shownin Fig. 17.A changein volumeof threesuccessive The control of the volume or intensity of a tone is tonesbut no changein volume during the sounding another important requirement in a synthesizer.A of eachtone is shownin Fig. 17A. A changein volume schematicdiagram of the volume controlsystem in the duringthe soundingof a tone is shownin Fig. 17B. electronicmusic synthesizeris shown in Fig. 16. The Many variationsof the effectsdepicted in Fig. 17 may amplificationof the push-pullamplifier is a functionof be obtainedwith the volumecontrol system of Fig. 17. the voltage applied to the No. ! grids. This voltage is suppliedfrom the combinationof a dc voltage supply, LOW-FREQUENCY MODULATOR a potentiometer,and a relay tree. In this manner a The vibrato is a complex modulation involving seriesof fifteen stepsin voltage can be obtained from either frequency,amplitude, or wave-formmodulation four circuits in the master control system. The use of or the combination of all three. is a term used the combinationof a potentiometerand a vacuum tube to designateamplitude modulation. In musicalinstru- eliminatesthe switchingtransients and ambiguitiesin ments and the voice the resultant low-frequency the relay tree duringthe actuationcycle. The resistance modulation termed "vibrato" or "tremolo" involves values of the potentiometerare selectedso that the the combinationof amplitude, frequency,and wave- over-all variation of the systemfollows an exponential form modulation. Therefore, the meansfor producing function. Input and output volume controlsare pro- the vibrato or tremolo in the music combines all three vided for presetting the volume range. The volume typesof modulation.The circuitdiagram of the system controlsystem controls the over-allvolume of the tone for producingthe vibrato is shown in Fig. 18. The circuit consistingof a gas triode employing a hot cathodegenerates a saw tooth wave. The saw tooth voltageis appliedto the grid of the push-pullcontrol tubes. The amplificationof these tubes is a function INPUT OUTPUT of the bias applied to the grids of thesetubes. There- o -o o I Ic

884 , / ',,./ ', ,,, ',,',,,,,, '302-20 / 4 ,8 I0ß 2 4 '/,/.8 I0 2 ,. 4 ,,.,.:.,,.8 IO FREQUENCY IN CYCLES PER SECOND Fro. 18. Circuit diagram of the electroniclow-frequency-modu- Fro. 20. Response-frequencycharacteristics of the variable lation system for introducing vibrato and tremolo. high and low passfilter systemof Fig. 19.

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A B

o - I . o

-30 -30 Io• • 4 8 •o3 • 4 8 •4 •oz •, 4 8 •o• • 4 8 •o4 FR EO• NGY FREQ U E NGY •m. 21. •ou• spectrumsof • s• •oo• •c •ing • fu•mc• f:c•uc•cy of • cyclesmo•;•c• •y •c fore, the over-allamplification of thesetubes varies in at componentscan be attenuated, thereby accentuating low rate and in a functionwhich approximatesa saw the fundamental and lower-order harmonics. tooth. Under theseconditions the resultantoutput is an In addition to the simple discriminatordescribed amplitude wave-form modulation of the incoming above,means must be providedin the electronicmusic audiowave with a largenumber of sidebands equally synthesizerfor accentuatingsingle harmonics or groupof spacedwith respectto frequency.The modulationis harmonicsand attenuatingsingle harmonics or groupsof of the orderof 6 to 7 cyclesper second. harmonics.This type of accentuationor attenuationcan be accomplishedby meansof the resonatorchain shown TIMBRE CONTROL in Fig. 22. The circuit diagram of one element of the The timbre of a tone dependsprimarily upon the resonatorchain is shownin Fig. 23. It will be seenthat overtone structure of the tone. In order to obtain tones this is a vacuum tube amplifier with a shunt resonant of differentovertone structures, means must be provided electricalnetwork in the plate circuit of the vacuum in the synthesizerfor varying the overtonestructure of tube. The two-stageamplifier employs voltage any tone producedby the synthesizer. so that the voltage output of the secondtube will be One of the most effective frequencydiscriminators practically independentof the impedanceof the load. is the combinationof a high and low passfilter system A typical responsefrequency characteristicof this with variable cutoff. A schematicdiagram of a high amplifiershown in Fig. 23 is shownin Fig. 24. Employ- and low passfilter systemis shownin Fig. 19. The ing a chain of theseamplifiers each tuned to a different responsefrequency characteristics obtainable with this frequency,it is possibleto obtainall mannerof overtone filter systemare shownin Fig. 20. A few typical ex- structures.Two typical examplesof the effect of the amples of the effect of the high and low pass filter resonator chain upon the spectrum of a saw tooth systemupon the spectrumof a saw tooth wave having wave having a fundamentalfrequency of 440 cycles a fundamental frequency of 440 cycles is shown in is shownin Fig. 25. It will be seenthat the funda- Fig. 21. It will be seenthat the fundamentaland low- mental, certain harmonics, or groups of harmonics frequency componentscan be attenuated and the can be eliminated by means of the resonatorchain. effect of the higher order harmonicsthereby accentu- This is equivalentto accentuatingother harmonicsor ated. It will also be seen that the high-frequency groupsof harmonics.

Fro. 22. Block diagram of a OUT chain of eight resonators.

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604 Fro. 23. Circuit diagram of one element of the resonator chain of Fig. 22.

0

OUT

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tional musicalnotation is also shownin Fig. 27. The holes in a continuoushorizontal line at the top of 20 Fig. 27 are not part of the record.These are shownfor comparisonpurposes, one hole having bee_npunched 1 _z15 by each of the keys. These holes are numberedlike the keys of Fig. 5 in the binary code numbering. Referring to Fig. 27, it will be seen that the coding on the left half is for one synthesizerchannel and the codingon the right for the other synthesizerchannel. Referring to the growth, duration, and decay coding, o IO• 2 $ 4 5 6 7 8 9 io4 it will be seen that the notes are executedalternately FREQUENCY IN CYCLES PER SECOND by the first and second channel. For illustration Fro. 24. Response-frequencycharacteristic of one purposes, Fig. 27 shows more changes in timbre, element of the resonator chain. growth, decay, and volume than would be the casein this musical selection. A schematicdiagram of the systemfor controlling the timbre is shownin Fig. 26. In this systemsixteen DISK RECORDER different timbre selections can be obtained from the When the paper record has been punchedand the four circuitsin the master control system. various elements of the synthesizer have been set,

CODED RECORD the next stepis a recordingof the output of the synthe- sizer. The elementsof the disk phonographrecording The paper record is punchedby means of the key- systemare shownin Fig. 28. A photographof a part of board punchingsystem shown in Fig. 5. The keys are the electronic music synthesizerincluding the disk colored to facilitate the operation of punching the recordingsystem and the interconnectedpaper drum codes.The note-selectinggroup of 1, 2, 4, and 8 are drive is shownin Fig. 29. The recordingsystem consists white. The octavegroup 1, 2, and 4 are red. The timbre of a lateral cutter and a conventional33« rpm turntable group1, 2, 4, and 8 are green.The growth,duration and driven by a synchronousmotor. The disk recorderis decay group 1, 2, and 4 are blue. The volume control coupledto the paper drum drive by meansof a flexible group 1, 2, 4, and 8 are yellow. cable. In this way the paper record is synchronized It will be seen (Fig. 5) that the punchedrecord with the disk record. consistsof rows of holes. Each row of holes passes The synthesizeris purposelylimited to the production under a brush. Each brush is equipped with several of two simultaneous tones. The reason will be evident springsarranged so that the brushnever breaks contact in the descriptionwhich follows.In general,due to the before making contact at the adjacent hole. Thus, a characteristicsof most musical sounds,the system is row of holeswill provide continuouscontact and at the actually limited to a seriesof single tones. That is, sametime give the sameresult as a slot in the paper. the system can simulate any single wind instrument, Slots cut in the paper will result in a very weak record such as a clarinet, saxophone,oboe, trumpet, etc., or that can be easily torn and with poor lateral rigidity. one string of a , such as a guitar, A simple punched record for playing a phrase of violin, etc., or one fingerplaying of a keyboardinstru- " SweetHome" is shownin Fig. 27. The record ment, suchas a piano,, organ etc. Thus it will is drawn to scaleand has the lengthindicated in inches. be seen that in order to simulate an ,each A paper speedof two inchesper secondis about the individual instrument must be coded and recorded correct speed to run the paper record through the separatelyand then the groupof instrumentscombined. machine panel. The correspondingphrase in conyen- In the case of keyboard instruments, the number of

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'3010•2 4 8I0 • 2 4 8I0' '•- 30• I0; 2 4 8 103 • 4 810' FREQUENGY FREQUENCY FTG.25. Soundspectrums of a sawtooth havinga fundamentalfrequency of 440 cyclesmodified by resonator chainfor two differentsettings of the resonatorchain of Fig. 22.

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FILTERS AND RESONATOR CHAINS OHANNEL I CHANNEL

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m m m m m m I I m I m I I I OUTPUT I I J_ O I -';' I • I 'iß *ß ***O0 ß : ß** 000 O0 ß I I I I ß moo oo ß ß ß oooo oo ß I I I I I ß O: OOß ß ß OO I • I - ß 0"0' O0 ß 0-- I ß •00 O0 ß ß ß ß O0 ß ß

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ß m ß O0 ß ß ß ß O0 ß •,,':•...... ,11 p-;.US.ES .•-PAPE..ECO.D-• DRUM • ,,.•,- •_ Fro. 26. Schematicdiagram of the timbre selectingsystem. separaterecords required will dependupon the number EV .... ER SO HUM-BLE of tonesthat soundedsimultaneously. The systemfor Fro. 27. The punchedpaper record. combiningthe differentrecordings produced by the synthesizerwill now be described.The sixteen-inchin Fig. 30. A photographof the disk recordingsystem disk record can accommodate six three-minute record- is shownin Fig. 31. In combiningthe individualrecords ings.After six completerecordings have been made, the levels can be adjusted by means of the mixers. whichrepresents six differentmusical renditions, the Employingthe systemshown in Figs. 28, 29, 30, and sixrecordings are combinedinto a singlerecording by 31, it is possibleto record 36 individual records.In meansof the double turntable recordingsystem shown the next step, the recordon the upper turntable con-

SYNTHESIZER CHANNEL I

AMPLIFIER

SYNTHESIZER CHANNEL 2

REOORD GROOVES

DISK REOORD

Fro. 28. Perspective view and sehcmatic diagram of the paper record and the disk recording systemof the music synthesizer.

CA BLE DRIVE

OABLE iRUSHES

ß ß ß

WORM : o GEAR o

ß PAPER RECORD

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Fig. 2. A photographof the completesystem is shown in Fig. 32. A photographof the disk recordingsystem, ::i•f•i!!::•...•...•:•ii::!:::.•....;:E4•::::..?:::...... •.•:::::.•,...... •!ii•...•i::.:..:....`.:•i::•i•?•:.`•.-..:-:•' •:- •:• ...... ' -'""'::•' ::':: ' -,-::•..•..::.,.•'•f• E-•-..'•:•.•.::•;. :•.--.-..•'•Xi•*::•-:-'-'•::*•:•::•:"::::' •'.-.• ½-:-'•: the keyboard, coded paper record, and cabinet racks

:•i•iiii•iiii::.:.....:..:...•iii:.:.•fi!::::::::iig.:•::::•`..`•..•;•ig.f•..`..•...ii:g.:....`.•i•.....`..•;•::•::•...•...:``.•`/•?•X•.•:•:....`..•?...`.:•....:...•J:...•:i•i??..•.:•::•;--. i•!i,i•...... ;:.:/•;.' -• '•,-?•ti •::• i•.•-".:- ':-:•"'•'• .:-•.u•:::*•*•*:•:::::•:'•'•'••••--•'••'...... •.••i .... :-•-.:.""..... -:----:-'::.--:-'-?'":':?;":'•::::•::•:-:•:•:•:'.:: •'•'• .- ß:•:'•-'-". one, two, and three, with some of the front panels removed,is shownin Fig. 29. A "close-up"photograph of the keyboard and coded paper record is shown in Fig. 5. A photographof cabinet racks four, five, six, -,••• .....•..-'•:•' •. ,. '---:.'...... -•x•E:ß...... ;:•...... i::.'-z:.-:-.•--..•:.-..::..,...:.•:...:., :-f•.':'..•-•.::-:• .•.•.•:. • ....•,;.•::::.. and seven,with someof the front panelsremoved, is •:'i' ' ', ?•:::'- •i,•iiiEi-'•..-.i.-'.'•-L.?..-i!..:...... -...f:.'.t::-•a•:E '"':::"Y.'ß...... •:: ...... ß,•'E,-: •:-E"-"::•::•-::' ?:-":E'*E•'":::-'::'.'."::'" • ;..• ' shownin Fig. 33.

RESULTS OBTAINED WITH THE ELECTRONIC MUSIC SYNTHESIZER

The electronicmusic synthesizerhas been used to ...... producesimulations of the voice and existingmusical instrumentsas well as entirely new musicaltones which ...... :...•::•::::::...... •-,-'&!.:•:.::?•!!':...... :::.:...... "•' ,-'•-%•.•.•.,:•:.: .... cannot be producedby the voice or existingmusical instruments. A few of the results obtained are as follows: Fro. 29. A photograph of the recorder,paper record drive, and half of the electronicsystem of the synthesizer. Simulations of Plucked, .Struck, and Bowed taining the combinationof 36 individual recordscan String Instruments be transferredto the lower turntable and the recording The work on simulatingthe pluckedstring type has processrepeated. In this next step 216 recordscan be been directed towards combiningthe desirablecharac- recorded.In this way any number of individual records teristicsof the tonesof the banjo and guitar. The tone can be recorded. produced is smoother and more pleasing than the There are many advantagesin the above system as conventional plucked string instrument in that the follows' Each individual synthesizedselection is a contact noise producedby the finger or plectrum separateentity and can be workedon until the operator againstthe stringdoes not exist in the tonesproduced is satisfiedwith the product.The levelsof the individual by electronicsystem. The work on the struck string selectionscan be adjusted until the optimum mixture type has been directed towards obtaining the most is obtained. The individual recordingsare always beautifulpiano type tones,that is, the correctbuildup synchronized.Unlike a group of musicians,once a and decay. In addition, more fundamental can be result has been obtained,it can always be duplicated. obtained in the low-frequencyrange than is possible

COMPLETE ELECTRONIC MUSIC SYNTHESIZER with a concertgrand piano. The objectionablenoise of the hammer striking the string together with mech- A block diagram of the completeelectronic music anismrattle of the pianodoes not existin the tonespro- synthesizerand disk recording system is shown in ducedby the electronicsystem. Violin type tonescan be

POWER AMPLIFIER

PRE

PICKUPS MIXERS

Fro. 30. Perspective view and a schematicdiagram of the elements of the rerecording system.

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simplematter to simulatethese instruments. However, considerableimprovements in the tonescan be produced by the electronic synthesizerbecause the wind noise can be eliminated and greater frequency ranges can be achieved. In the low-frequencyinstruments it is possibleto obtain adequate fundamentalswhich are lacking in the ,contrabassoon, and sarruso- phone. In addition, much higher frequencyranges are possiblethan in the conventionalinstruments.

Simulations of Percussion Instruments

The work on simulating percussion instruments includesboth the definite and indefinite pitch types. The tones producedby bells, orchestrabells, glocken- spiel, and xylophoneare objectionablefor two funda- mental reasons- first, because the strike tones are FIG. 31. A photographof the recordingand disagreeableand, second, because the overtones are rerecordingsystem. not harmonics. These objectionablefeatures are not present in the tones producedby the electronicmusic produced,incorporating both vibrato and portamento. synthesizer.Drum type tones can be produced with In this case the bow scratch which has always been definite pitch, as in the caseof the timpani, but with a objectionablein the violin and other instrumentsof the much greater frequencyrange. Drum type tonesof the viol family doesnot exist in the tonesproduced by the indefinitepitch can be producedranging from the electronic system. The fundamental of the double to the . The use of the hiss basshas alwaysbeen inadequate.This limitation does generator and mixtures of the frequency generator not exist in the electronicsystem simulationof this make it possibleto simulate any existing percussion instrument. instrument and, in addition, an indefinite number of new percussionsounds. Simulations of Wind Instruments Simulation of the Singing Voice The work on simulatingwind instrumentsincludes air-, mechanical-,and lip-reed types of wind instru- The work on simulating the singingvoice has been ments. The essential difference between the different restricted to simple musical selections.The singing groupsof instrumentsis the growthcharacteristics and voice has been synthesized;one or more voices sepa- the overtonestructure. Therefore, it is a comparatively rately and in combinationwith a synthesizedorchestral

FIG. 32. A photographof the completesynthesizer and recorder.

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FIG. 33. A photographof the secondhalf of the synthesizerwith someof the panelsremoved. .The time spent on this phase of the synthesizer.However, to make a practical demon- synthesishas been very much less than on the instru- stration, it is necessary to train an operator or mental simulations.Nevertheless, this work has shown synthesist.In this connection,the music synthesizer that it will be possibleto simulate any singingvoice. is an entirely new genusof apparatus.Were it merely The fidelity of the simulation will be limited only by an improvement of existing species,immediate com- the degreeof perfectionachieved in the analysisand mercial applicationswould be evident. One of the uses synthesis. foreseenfor the musicsynthesizer is to make musicfor sale in the form of phonographrecords. To make an Simulation of the Speaking Voice artistic record,or a hit, novelty or technicalexcellence alone is not sufficient. There are other ingredients, The work on simulatingthe speakingvoice includes many of whichare intangible.However, the synthesizer the fundamentalfrequency ranges of both men and will facilitate the productionof sucha hit. For example, women. The work on synthesizingthe speakingvoice the synthesizercan produceany kind of sound that has been carried out to show the versatility of the can be imagined.Then if a personcan imagea hit, then synthesizerand to provide somepractical data in the the synthesizerwill facilitate the productionof the hit. field of speechcommunication. For example,the work The hit-producing attributes are not amenable to on speechhas shown that intelligible speechcan be analysis in the acoustical laboratory, so this factor synthesizedfrom a very simple code, that is, 525 bits must be left out. To demonstratethe possibilitiesand per second. Theoretically, the information could be performanceof the synthesizer,an experiment was transmittedon a channelwith a frequencyband width conducted as follows: of 78 cyclesand signalto noiseratio of 20 db. Two different piano selections,namely, "Polonaise Proof of Performance In A Flat, Opus 53" (Chopin), "Clair de Lune" (De- bussy), a violin and piano selection,"Old Refrain" The characteristics of a tone are known and have (Kreisler),all playedby famousartists and reproduced been outlined in the first part of this paper. From this from disk records were compared with synthesizer fundamental knowledge and the characteristicsand versionsof the same selections.The piano selections performanceof the synthesizer,as outlined, it is not were played by Iturbi, Rubenstein,and Horowitz and difficultto provefrom theorywhat can be donewith the violin in "Old Refrain" was played by Kreisler.

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The synthesizer versions, completed on August 5, is limited to the useof ten fingers,two hands,two feet, 1953, and the identical passagesfrom the phonograph and the lips, either separately or in various combina- recordswere recorded on , intermixed, tions, to perform the different operations. These and played to various people.They were asked to tell limitations do not exist in the synthesizer. which was synthesizedand which was not. Interpreting The experimentin the precedingsection illustrates the results by standard statistical methods, it can be another use for the electronic music synthesizer, saidwith 70 percentcertainty that only oneout of four namely, the rejuvenation of old recordingswhere the personscan tell which is which. master is in poor condition. The old record can be It shouldbe noted that this work was donewith only analyzedand synthesizedto producea replicaof the old the helpof conventionalequipment to aid in the analysis record but without distortion or noise. which is not as complete as demandedfor synthesis; The experiment of the precedingsection illustrates thus much of the work was done by cut and try. This still another use of the electronic music synthesizer, points to an important feature of the synthesizer. namely, the production of new musical renditions Manual dexterity is not required. A synthesisonce synthesizedto simulate the performanceof an artist learnedcan be added to the fund of knowledgewithout who has ceasedto perform. Both voice and instru- further practice to be able to perform it. The ability mental musicalselections may be synthesizedfrom an of the synthesist is, therefore, always increasing. analysis of the style and structure obtained from If a composerhas in mind what he wants to achieve, information containedin recordingsproduced by the the effectscan be obtainedby meansof the electronic artist past. If the artist is alive, but is unable music synthesizer,regardless of whether he can play for physical reasonsto perform, he can supervisethe a musicalinstrument or not. The composeror musician synthesis.In this way, becauseof the inherentphysical can producethe soundof any existingmusical instru- versatility of the electronic music synthesizer, there ment as well as other sounds,regardless of whether is the possibility of obtaining artistic effects that he they have ever existed.The resultswhich the composer could not achieveeven at the peak of his performance. and musician wishes to achieve can be obtained and If the artist is dead, the style and characteristicsof the demonstratedas the music is being composedand artist may be analyzedfrom his recordsand catalogued played. Once a particular result has been obtained, it for use in simulatingthe performanceof the artist by can be retained forever. Thus, it will be seen that the synthesis.The product of the electronicmusic synthe- electronicmusic synthesizerprovides a powerful tool sizer may be supervisedand monitoredby a musician for the composeror musicianbecause he can reproduce to insure that authentic results are obtained. or create any sound or combinationof soundswhich There are many other usesfor the synthesizerin the have or have not been produced,that may have any field of communication,but it is beyond the scopeof musicalsignificance. this paper to outline all of the significantapplications The foregoingexperiment demonstrates the potential of the electronicmusic synthesizer. capabilitiesof the synthesizerin the ability to copy existingselections. For an acousticalengineer to copy Complete Synthesized Renditions of Musical the performanceof famous artists in the matter of a Selections few weeks shows the tremendouspossibilities of the synthesizer.For example, it would be impossiblefor One use envisionedfor the electronicmusic synthe- even a geniuswith no previousexperience in playing sizer is the productionof music for sale in the form of a musical instrument to imitate all of these artists on phonographrecords. In order to demonstratefurther these two instrumentswith the order of fidelity that the potentialities of the electronicmusic synthesizer, was achieved. Thus, it seems quite obvious that a completemusical selections were synthesized.A partial trained or professionalmusician could produce great list of the synthesizedmusical selections,indicating musical renditions by means of the electronicmusic the style of the rendition and the date on which the synthesizer. synthesiswas completedfollows' APPLICATIONS OF THE ELECTRONIC MUSIC "Blue Skies"(Berlin), April 1, 1952.In the style of a SYNTHESIZER dance band. Among the usesfor the electronicmusic synthesizer "Nola" (Arndt), May 28, 1952. In the style of the is the production of phonographrecords and other piano. types of recordedmusic. The use of a synthesizerfor Stephen Foster Medley, December 12, 1952. "Oh the productionof musicalsounds opens a new field for Susanna," "De Camptown Races," "My Old the productionof recordedsound. For example, there Kentucky Home." "Old Black Joe," "Old Folks is the possibilityof producingentirely new tone com- at Home," and "Hard Times ComeAgain no Mo." plexesand combinationswhich cannot be achievedin In the style of bowed,plucked and struck instru- conventionalmusical instruments.Furthermore, in the ments; air, mechanicaland lip reed instruments; case of conventional musical instruments the musician and percussioninstruments,

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"Holy Night" (Adam), December15, 1952. In the "Spoken Voice", March 26, 1954. A few spoken styleof the organ. sentencessynthesized to showthe versatilityof "FugueNo. 2 fromWell Tempered " thesynthesizer. (Bach), July 15, 1953. In the style of ancient struck and plucked strings in several variations. "HungarianDance No. 1" (Brahms),September 3, The resultsobtained with the electronicmusic 1953.In thegypsy style without copying any synthesizerasexemplified bythe musical selections particular instrument,but varying colorsadapted foreasy synthesis. outlinedabove demonstrates thatexcellent musical "Sweetand Low" (Tennyson-Barnby), January 15, performancecanbe produced by meansof thisnew 1954.Voice and instrumentalaccompaniment to system;infact, the performance of the musical synthe- showthat voicecan be synthesized. sizerspeaks for itself.

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