DOEPFER Dark Energy - VCF Module Description

Thecutofffrequencyofalowpasslterde-
pending on the control voltage
Theresonancecharacteristicsofalowpass
lter
14
Dark EnerGy
DOEPFER
Functionality
3.2.2. VCF
Filtersareaveryimportandtoolineveryanaloguesynthesizer.Filtersmodifysoundsbyrejectingsome
frequencieswhileallowingotherstopassthroughinordertomanipulatetheharmoniccontentofthesound.
Therearedifferenttypesoflters;themostcommonandmostmusicallyusefulltertypeisthe24dB‘low-
pass’,whichisusedinDarkEnergy.Accordingtothistermination,alowpasslterpassesallfrequencies
belowthesocalled„cutofffrequency“andrejectsfrequenciesabovethecutoff.Thispointcanbecontrolled
byaknobormodulatedbyacontrolvoltageinordertoachievedynamictimbres.
Anotherimportandltertermis‘resonance’.Theresonancefunctionemphasestheovertones(orharmo-
nics)closetothecutofffrequency.Thesoundbecomesmoreandmore„sharper“.Atacertainlevel,the
lterstartstoselfoscillateandgeneratesawaveformclosetoasinewave.DarkEnergy‘sVCFcanalso
bedrivenintoselfoscillationinodertouseitasanadditionalsignalsourcetoprovidecertain,verypopular
sound effects.
TheVCFprovidesthefollowingcontrols:
•Manualfrequencyknob(Freq.)
ThisknobmanuallycontrolsthecutofffrequencyoftheVCF.Inotherwordsyou
„open“and„close“thepass-through„window“ofthelter.Atfullyclockwiseposition,
thelteriscompletelyopenedandtheentirefrequencyrangeoftheincommingsignal
ispassedthrough.Atfullycounterclockwiseposition,thelterisclosedsofar,thatall
audiblefrequenciesarerejectedandnooutputsignalisaudible.Theentirefrequency
rangeofDarkEnergy‘sltercoversapprox.12octaves.Themorethisknobisturned
intoclockwisedirection,thesmalleristheeffectoftheenvelope(ADSR)tothesound.
•XMknob
Inordertoachievedynamicandperiodicchangesintimbre,thecutofffrequency
canbemodulatedviacontrolvoltages.TheXMknobsetsthemodulationdepth.Set
fullycounterclockwise,nomodulationappears,whilefullyclockwisepositionmeans
maximum modulation depth. The modulation depth is added to the setting of the
manualfrequencyknob.Sincethesumofbothcannotexceedthemaximumvalueof
thecutoffparameterrange,thesettingofthe„Freq.“knobinuencesthemodulation
depth:Thehigherit‘ssetting,thelowertheeffectoftheXMknobtothesound.The
XMfunctionusesexponentialfrequencymodulation.
Insomecases,theFMhastobecontrolledinaveryneway,especiallywhenthel-
terisselfoscillating(resp.workingasasinewaveoscillator)andmodulatedbyLFO2
intheaudiorange.Inordertooptimizetheparameterscaling,theXMknobworksin
anexponentialway.Thus,audiblemodulationmightneedsettingsabove„5“,espe-
ciallywhenusingtheADSRasamodulationsource.
f
c
CV
tuOtuO
.qerF.qerF
f
c
Resonance changes the lter characteristics
f
c
Resonance
Frequency
0 db
Attenuation