synthesizer basics
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full explanation of basics of syntheszisersTRANSCRIPT
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Postedby: DonSolaris On: March18,2014 2
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Synthesizer basics
ThestructureStructureofalmostallsynthesizersisbasicallythesame.Itstartswiththetonegeneratorwhosefunctionistocreatethesound.Onanalogsynthesizers,thisgeneratorisasimpleoscillatorcircuit,whichcangeneratefewbasicwaveformslikepulse,saworsinewave.Thereforeonanalogsynthesizersitismorecommontousetermoscillatorthantonegenerator.Ondigitalsynthsusedtermsare:wavegen,wavegenerator,tonegenerator,andsometimes,evenanoscillator(thoughitisnotarealoscillatorinside).
Nextcomesthefilterwhichdefinesthetimbreofthesoundandadds/removesharmonicsfrom
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Nextcomesthefilterwhichdefinesthetimbreofthesoundandadds/removesharmonicsfromtheoriginalsoundcreatedinoscillator.Filterisfollowedbyanamplifier,inwhichyousetupvolumechangeofthesound.EnvelopesandLFOsareusedtomanipulatevarioussettings.Forexample,inoscillatortheycancontrolitspitch.Infiltertheycandefinefilterchangesoverthetime.
Thiswasthebasicdescription,howevereachsynthcanhaveitsownandmorecomplicatedstructure.ImageaboveshowsusthestructureofRolandsXVsynthesizer.Eachpatchcancontainuptofourtoneseachwithitsownsettings(sounds).Patchalsocontainscommondata,whichconsistsofparametersthatapplytoallfourtoneslike:patchname,overalllevel,octaveshift,keymode(mono/poly),portamentosettings,benderrangeandmore.Patchalsocontainsmodulationcontrol(matrixcontrol)inwhichyouspecifywhichcontrollerwillchangewhich
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modulationcontrol(matrixcontrol)inwhichyouspecifywhichcontrollerwillchangewhichparameterforexamplemodwheelonthekeyboardtochangeamountofcutoffandresonanceofthefilterorthepitchofthewavegenerator(WG).
OscillatorThepurposeofoscillatoristoproduceasoundthatyouwilllaterprocesswithafilterandamp.Onceyoupressthekeyonthekeyboard,youactivatetheoscillator(inanaloguesynthesizeritisactuallyalwayson).Oscillator(OSC)isthestartingpointofanysynthesizer.Itisaplacewherethewaveformisbeingcreated.Inanalogsynthesizer,oscilatorcanbedigitally(DCO)orvoltagecontrolled(VCO)anditusuallyproducespulseorsawwaveofwhichpulseswidthcanbecontrolledandevenmodulated(PWM).Alloscillators,nomatterforwhatapplication,workinthesameway.Ifwelookattheirheartwillfinditlookssomethinglikethis.
Tobedescribedinthesimplestway,oscillatorisanamplifierandafilterthatoperateinaloop.ThebasisofoperationisthetunedresonantcircuitforexampleLCcircuitthatismadeofinductor(L)andcapacitor(C).Inthiscircuitvoltageandcurrentvarysinusoidallywithtimeandare90degreeoutofphase.Thereareinstantswhenthecurrentiszero,sotheenergystoredininductoriszero,butatthesametimethevoltageacrossthecapacitorisatitspeak,whileallofthecircuitsenergyisstoredintheelectricfieldbetweencapacitorsplates.Therearealsoinstantswhenthevoltageiszeroandthecurrentisatapeak,withnoenergyinthecapacitor.Then,allofthecircuitsenergyisstoredintheinductorsmagneticfield.Asyoucansee,theenergystoredinthiselectricalsystemisswingingbetweentwoforms.Unfortunatelythisswingingwontgoforeverduetocircuitlosses.Conductorshavesomeresistance,aswellascapacitorandinductor.Thatisthereasonwhyweneedamplification.Thegoalofthisamplificationisnottoaddsomehighgain,butjusttocompensatethelosseswehaveinLCcircuit.Youcanimagineoscillatorlikependulum,whichduetodragandfrictionlooseitsmovementenergy,soyouneedtokickitfromtimetotime.
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Attheoutputofoscillatorwecanhavevariouswaveforms,dependingonthetypeofoscillatorthatwebuilt.Forexampleifouroscillatorisproducingasinusoidalwave,wecallit:sinewaveoscillator.Therearemanytypesofoscillators,mostknownareshownonimageabove,andthoseare(fromlefttoright):sine,triangle,squareandsaw.Squareisactuallyapulsewave,with50%width.
WavegeneratorDigitalsynthesizershaveadifferentkindofoscillatorintheirheart.Itisnotaclassicoscillatorthatwejustdescribed,butadevicethatusesPCMwaveforms.Pulsecodemodulation(PCM)isadigitalrepresentationofananalogsignalwherethemagnitudeofthesignalissampledregularlyatuniformintervals,thenquantizedtoaseriesofsymbolsinabinarycode.Ifyouhavesomewavfilesonyourcomputer,thosearethePCMwaveforms,thesamethatareinyourdigitalsynthesizer.Advantageofdigitalwavegeneratoristhatitisnotlimitedtobasicwaveforms(sine,saw,square,etc.)butcancontainanykindofdatathatwaspreviouslydigitized.Youcanhaverealpianosamples,guitars,drums,etc.Ofcourseifyouwantyoucanhavebasicwaveformstoo.Mostdigitalsynthshaveatleastasineandasawwavesampleinsidetheirwaveformmemorysoyoucancreatesomeanalogsoundingtonestoo.
Nowyoumightask,whyoneneedsanalogsynth,whenthesametypeofwavescanbecreatedwithdigitalPCMwavegenerator.Theanswerwasactuallyjustsaidisintheprevioussentience,itisawordPCMgenerator.Eachtimeyoutriggerthistypeofgenerator,itwillproduceexactlythesamesoundingwaveform.Resultisuniformtonethatstaysthesame.Incontrast,analogsynthesizershaveimperfectoscillators,whichresultinvarioustypesoffluctuationsthataredifferenteverytimeyouhitthekey.Inasensetheysoundunpredictedanddifferentoneachotherkey.Butthatisjustthebeginningofthestory.Onceyouengagepulsewidthmodulation,thereisnodigitalPCMsynththatcanenterthisarea.Thencomestheanalogfilter,whichagainaddsitsowncharacter.Inshort,thisisoneofthereasonwhy30yearoldsynthesizersusuallycostmorethanthelateststateoftheartPCMdigitalsynthesizerwith9000patches.
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Itisimportanttounderstandthatwetalkabouttwodifferentworldshere.Itwouldbeprettynaivetoblamesomedigitalsynthandcallitpoorbecauseitcantdosomegoodanalogsounds.IfsomeoneaskswhyaPCMsynthcantmakeasuperthunderingMoogbasssound,thesimplestanswerisitwasneverdesignedtoso.
FilterThemostdramaticchangeofyoursoundistakingplaceinthefiltercircuit.Therichertheharmoniccontentonthewaveform,themorethechange.Exampleofrichharmonicwaveformswouldbesquareandsawwave.Ifyoursynthesizerdoesnothappentohaveresonantfilter,youareactuallymissingonereallyimportantandcharmingaspectofasynthesizer.
Ifwelookatfrequencydomainofasound,forexamplesquarewavewhichisrichinharmonicsandplayalownoteatsay20Hz,wecanseethattheseharmoniccomponentsarespreadinthewholeaudiorange(20Hzto20kHz).Whatfilterwilldoistoisolatesomepartsofthisrangeinordertoaccentuateitsotherfrequencies.
TypesoffiltersThemostknowfilteristhelowpassfilterLPF.Itreducesthevolumeofallfrequenciesabovethecutofffrequency.Youcanspecifythiscutofffrequencyinfiltersettings.Onceyoucutouthighfrequencyrange,thesoundwillbecomemoremellow.
NexttypeoffilterwidelyknownisahighpassfilterHPF.ItisdoingexactlyoppositethingfromLPF.Itcutsthepartofthespectrumwhichisbelowthecutofffrequency.Itcanbeusefulforpercussivesounds(niceanalogsoundinghihatscanbemadewithit).Highpassfiltercanberesonanttoo,butactuallytherearenotsomanysynthesizersthatfeatureit.KorgMS20oneof
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resonanttoo,butactuallytherearenotsomanysynthesizersthatfeatureit.KorgMS20oneoftherareanaloguesynthsthatfeaturesanalogresonanthighpassfilter.
AnoneofthemostspecificsoundingfiltersisprobablythebandpassfilterBPF.Thisfilterleavesonlytheregioninthevicinityofthecutofffrequency,andcutstherest.Withresonancesettingyouareactuallyshapingthewidthofthisfilter.Themoreresonance,themorenarrowthisfilterwillbe.Imagebelowshowsfrequencyresponseofthreebasicfiltertypeswejustdescribed.
ResonanceOnceyouactivateresonanceonalowpassfilter,newharmonicswillpopupinthelowerrange,creatingnewsoniccomponentsthatdidntexistinoriginalsound.Highlevelsofresonancecanproduceselfoscillation.RolandsJunomanualhasaveryinterestingandspecificexplanationofresonance(ifinditreallyfuntoreadittoday,butactuallyitisagoodexplanation):Thiscontrolemphasizesthecutoffpointsetbycutofffrequencyknob.Asyouraisetheknob,
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Thiscontrolemphasizesthecutoffpointsetbycutofffrequencyknob.Asyouraisetheknob,certainharmonicsareemphasizedandthecreatedsoundwillbecomemoreunusual,moreelectronicinthenature.Ifyoualterthecutofffrequencywhiletheresonanceknobissettoahighlevel,youcancreateatypeofsoundthatisattainableonlyfromasynthesizer.RolandJuno106Manual
Filterpoles/slopesSometimesyouwillreadthatafilteris4poletype.Thisisjustanothertermfor24dBfilterslope,whichisthemostcommonfiltertypeintheworldofanaloguesynthesizers.Numberofpolesdefinesthesharpnessofthefilter.Themorepolesfilterhas,thesharperitsfrequencyresponsewillbe.Thisalsoaffectstheresonance,sincesharperfilterresultsinmorepowerfulsoundingresonance.RolandTB303usesthenotsocommon,18dBfilterslope.Nowyoumightwonder,whatthis18dBmeansanyway.Itisaunitwhichtellsyouhowmuchafilterwillblockperoctave.Whichinthiscaseis18dB.Ifyouputafiltercutoffpointto440Hz,oneoctaveaboveat880Hzsignalwillbeattenuatedfor18dB(whichisabout63times).
Ifafilteris4pole,thesignalwillbeattenuated24dB,whichfor440Hzcutoffpointmeansthatthesignalon880Hzwillbeabout255timesweaker.Imageaboveshowsattenuationcurvesoffourfiltertypes:6dB,12dB,18dBand24dB.
Whichfiltershouldyouuse?Thechoiceisuptoyou.Ifyouprefernicesmoothfiltersweepsounds,youshoulduse12dBfilterwithagoodresonancevalue.Forthunderingbasssoundsorhighresonancezapsyoushoulduse24dBfilter(fullresonanceforzaps).While6dBfilterisgenerallynotused,itcomeshandforsampleplayback,togentlyremovehighendfromtheharshsoundingsamples,whilenottotallydistortingthephaseofthesample.
AmplifierandenvelopeLaststageofsoundmanipulationthatistakingplaceinthesynthesizerishappeningattheamplifiersection.Itspurposeistocontrolvolumechangesofthesound.OnanalogsynthesizersamplifierisusuallycalledVCA(ifitisvoltagecontrolled)orDCA(ifitisdigitallycontrolled).On
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amplifierisusuallycalledVCA(ifitisvoltagecontrolled)orDCA(ifitisdigitallycontrolled).OndigitalsynthesizersamplifierisusuallycalledAMPorincaseofRolanditiscalledTVA,whichstandsfortimevariantamplifier.MainpartoftheamplifieristheADSRenvelope.
ADSRenvelopeThisstandsfor:Attack,Decay,Sustain,Releaseanditrepresentsfourpoints.Onceyouhitthekey,youareattheattackpoint.WithAttackyouaresettingamountoftimethatitwilltakeforsoundtoevolvefromitsstartinglevel,tothepointwhereyoupressthekey.ThisisfollowedbyDecayinwhichsoundcanevolvetoanotherlevelthatyouset.ThisisfollowedbySustainpoint.Aslongasyouareholdingthekeypressed,youareatsustainpoint,andthelevelyousetatsustainpointwillbethelevelofthesoundduringthetimethekeyisheld.Onceyoureleasethekey,thesoundwillgooff.TopreventthesoundfromgoingawaytosoonyoucansettheReleasepoint.Releasesetstheamountoftimeitwilltakeforsoundtogettozerolevel,afteryoureleasedthekey.
Thereareenvelopeswithmorethanfourpointsthatwedescribed,buttheyallworkinthesameway.Rolandstypicalenvelopeconsistsoftwodecaylevels.SomeYamahasSYseriessynthssuchasSY77andSY99havelooppointsthatyoucansettotheenvelopewhichisprettycoolfeature.
LFOandcontrolThepurposeofLFOistoaltervarioussoundsettingsinback/forthcyclicmanner.UsuallyLFOcanapplychangetooscillatorspitch,filtercutofffrequencyandamplevel.IfyouapplyLFOtothepitch,youwillgetvibrato,ifyouapplyittofilter,yougetsweepingsound(suchaswahwah),ifyouapplyittoamplevel,yougettremolo.
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Asitsnameimplies,LFOisanLowFrequencyOscillator.Usuallyitconsistsofafewbasicoscillatorwavetypeslikesine,saworsquare.YoucanimagineLFOlikeahelpingdevice,whichishelpinginwaythatyoudonthavetomanuallychangethepitchorlevelofthesound.InsteadyouprogramLFOtodothat.Howeverifyoudowishtochangesomesettingmanually,thenyouneedtospecifythemincontrollersection.
Audioexample1:Toneslevelmodulation.Clickheretohearoriginalnonmodulatedsound.LFOwassettomodulateamplifier(tonelevel).LFOswaveformwassinewave.Resultcanbeheardhere.
Thetwoimagesaboveshowamplitudeasafunctionoftime(waveformdisplay).Asyoucanseeoriginalsoundhadconstantlevel(amplitude).OnceweappliedLFO,levelstartedtomodulatefromminimumtomaximumvalue.Shapeofthesinewavethatwasmodulatingoriginaltonecanbeclearlyseenonsecondimage.
Audioexample2:Tonesfrequencymodulation.Clickheretohearoriginalnonmodulated
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Audioexample2:Tonesfrequencymodulation.Clickheretohearoriginalnonmodulatedsound.LFOwassettomodulateoscillatorspitch(frequency).LFOswaveformwassinewave.Resultcanbeheardhere.
Imageaboveshowsfrequencyasafunctionoftime(spectraldisplay).ItcanbeclearlyseenhowappliedLFOmodulatesthepitch(frequency)oftheoscillator.Shapeofthesinewavethatwasmodulatingoriginaltonecanbeclearlyseen.Originaltonewasfixedfrequencyat440Hz.OnceweappliedtheLFO,tonestartedtovarythepitchforabout50Hzaboveand50Hzbeloworiginalfrequency.
ControlMostofdigitalsynthsofferyoutoapplyvariouscontrollerslikemodwheel,aftertouchorvelocitytosomeofthesoundsparameterslikefilterscutoffpointorresonance,soundlevel,etc.Somesynthscallthisfeaturemodulationmatrix.Itgoessomethinglikethis.Firstyouspecifythesourceofthecontrollerforexamplemodulationwheelonthekeyboard.Thenyouspecifyitsdestination,forexamplefiltercutofffrequency.Nowyousettheamount,andyouarereadytomodulatethefilterwithmodulationwheel.Iffiltersettingsonthesoundareonthemaximumopenposition,thenyouneedtoapplynegativevaluetothecontroller,sothatwhenyoustarttomovethewheel,filtergetsclosed,fortheamountyouspecified.SomebettermodulationmatrixsystemswillallowyoutoapplyalmostanysynthfeatureasasourcetomodulateitsdestinationforexampleLFO1tomodulatespeedofLFO2whichcanresultinverycomplexandunpredictedresults(thisisincasethesynthhastwoLFOs).Thisistheareathatrequiresalotofexperimenting,butresultsarealwaysrewarding.
Abbreviationsandcommonterms
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Circuitbendingischanging,removingoraddingnewelectroniccomponentswithinsynthesizertoachievedifferentperformancethatisunavailableinoriginalversion.Usuallycheapsynthsarebeingcircuitbenttosoundmorewild,unpredicted,strange,oralltogether.Circuitbendingresultswithwarrantyvoid,andcandamageyoursynthpermanently.
Legatoisafunctionthatshouldonlyworkinmonophonicmode.WhenLegatoison,pressingonekeywhenanotherisalreadypressedcausesthecurrentlyplayingnotespitchtochangetothatofthenewlypressedkeywhilecontinuingtosound.Thiscanbeeffectivewhenyouwishtosimulateperformancetechniquessuchasaguitaristshammeringonandpullingoffstrings.
Modulationwheelaffectsthesoundasspecifiedbythecontrolparameters(controlmatrix).Onmanysynthsitissettovibratobydefault.
Portamentoisafunctionthatcausesthesoundspitchtochangesmoothlyfromonenotetothenextnoteplayed.Portamentoiscommononguitar,violinandotherstringinstruments.However,portamentoisnotpossibleonafixedpitchinstrumentlikethepiano.Onasynthesizer,parametercalledportamentotimeorportamentospeeddefinesthespeedatwhichanoscillatormovestoanewnoteyoupressedonthekeyboard.WhentheKeyAssignModeis
mono,thiscanbeeffectiveinsimulatingperformancetechniquessuchasaviolinistsglissando.
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mono,thiscanbeeffectiveinsimulatingperformancetechniquessuchasaviolinistsglissando.
Pitchbender(pitchwheel)bendspitchoftheplayednoteupordown,andisspringloadedtoreturntocenterposition.
Comments (2)
Great DepressionOctober18,2014at23:21
Goodblogyouhavehere..Itshardtofindqualitywritinglikeyoursthesedays.Ireallyapppreciateindividulslikeyou!
Takecare!!
Don SolarisDecember2,2014at21:09
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