DOEPFER Dark Energy - Page 28

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Dark EnerGy
DOEPFER
Basics of Soundgeneration
frequency.Forthegivenexamplethiswouldresultin:1000Hz,1400Hz,11800Hz,200Hz,etc...
Strictlyspeakingthisonlyappliestopuresinewavefrequenymodulation,i.e.ifboth,VCOandLFO,
aresinewaveoscillators.Withotherwaveformsadditional(non-)harmonicswillbeadded.Unhar-
monicsounds,similartofrequencymodulation,arealsoproducedbypulsewidthmodulationwith
highfrequencies.Inpracticethispricipleisusedforcreatingextreme,unharmonicsounds.Thede-
greeofbeingunharmonicdependsonthestrength(amplitude)ofLFOmodulationaswellasonthe
frequencyratioofVCOandLFO.“Practiceisbetterthantheory”applieshere.Youshouldtryvarious
settingsforLFOfrequencyandLFOamplitude.Mostprobablytheresultingwaveformsarenotsuited
forsweet,“beautiful”soundsbutcanbeusedforextreme,“vigorous”soundsinstead.
Filters
Withsubtractivesoundsynthesisthefurtherprocessingofthetonal“rawmaterial”(VCOsignal)will
bedonebyavoltagecontrolledlter(VCF)rstwhichisusuallyfollowedbyavoltagecontrolled
amplier(VCA).
There are different typesorcharacteristicsoflters.The
basictypesarelowpass,bandpassandhighpasswhilethe
typesnotchandallpassarelesscommon.Theltertypes
differinhowtheyfeedthefrequencythroughresp.which
frequencyrangesarerejected.Alowpasspassesallfre-
quenciesthatarebelowthecutofffrequencyandcutsoffall
frequenciesabove.Thehighpassworksjusttheopposite
waysinceitpassesallfrequenciesthatareabovethecutoff
frequencyandcutsoffallfrequenciesbelow.Abandpass
passesallfrequencieswithinacertainrange(band)and
rejectsallfrequenciesoutsidethisrange.Anotchcutsouta
certainfrequencyrange(inversefunctionofthebandpass).
Anallpasspassesallfrequenciesbutitperformsaphaseshiftdependantonthefrequency.Formusi-
calpurposesthelowpassisbyfarthemostefcientltertype,thusitisusedinDarkEnergy.
Nexttotheltertype,anotherimportantparameterofalterisslopewhichismeasuredindB/Oc-
tave.Itdescribeshowsteepthetransitionfrompassingtorecectionoccurs.The“ideal”lterwould
haveaninniteslope,i.e.thetransitionoccursimmediately(e.g.999Hzwouldpasstotallywhile
1000Hzwouldbesupressedtotally).Inrealitythistransitionisnotajumpbutagliding,depending
onthelter’sslope.Formusicalpurposes,alterwithahighvaluewouldhaveaslopeof24dB/Oc-
tavebut12dB/Octavearealsousefulforspecialapplications(usuallyforhighpass,bandpassand
notch).DarkEnergyusesa24dB/Octacelter,sinceitworkedouttobethemostmusicalusefuland
efcient.
Afurtherlterparameterisresonance(oremphasis).Ifthe
lterprovidesanadjustableresonance,frequenciesclose
tothecutoffpointcanbeemphasized.Thelterbecomes
moreofabandpasswithanunderlaidlowpass.Formusi-
calapplicationsitisveryimportantthatthelterresonance
isabletobeadjusted.VCFswithoutadjustableresonance
are seldomly used. Overtones close to the cutoff point are
emphasizedthebiggertheresonanceisset(seeg.XX).
Thisresultsinthetypicalresonanceandtweetsoundsof
ananaloglter.Withmanylterstheresonancecanbeset
tosuchahighdegreethatselfoscillationofthelteroccurs
(evenwithoutanyinput).Thisallowsyoutousethelteras
asinewaveoscillatorinsteadoftheVCOforspecialpur-
poses.Youguessedit–alsoDarkEnergy’slteriscapable
to self oscillate and thus to create a lot of typical sounds.
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Resonance changes the lter characteristics
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Resonance
Frequency
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Attenuation
Charakteristicsofalowpasslter