ER-301/Evil Twin

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Dual Oscillator FM/PM/AM Synth


Evil Twin is a dual oscillator FM/PM/AM synth that you can load up, assign a V/oct pitch signal and a gate signal and start using immediately. There is no other patching required so you can literally download and start making interesting sounds with your ER-301 without knowing anything about FM, PM or AM synthesis. Just play around with the top level controls and have fun!

The following diagram illustrates the signal flow and how the local controls map to the parameters and units inside this custom unit. Each of the controls is described in the Controls table below

EvilTwin Schematic v0.7.png

If you have any questions then visit the Evil Twin forum thread where Kel or Joe (the people who programmed this custom unit) or someone else will be able to help you.


Save​ ​the​ ​Custom​ ​Unit​ preset ​(File:Evil Twin.lua)​ anywhere on​ ​your​ ​SD​ ​card.​ ​​ To use it, you will need​ ​to​ ​insert​ ​an​ ​empty​ ​custom​ ​unit​ ​in​ ​your​ ​patch,​ ​then​ ​load​ ​the​ ​Evil​ ​Twin​ ​preset​ ​into​ ​that custom​ ​unit.​ ​​

Pitch,​ ​Gate,​ ​and​ ​Amp​ ​Envelope

Connect​ ​your​ ​pitch​ ​v/o​ ​input​ ​to​ ​the​ ​​v/o​​ ​control​ ​by​ ​pressing​ ​it​ ​and​ ​choosing​ ​an​ ​input​ ​(A1-D4). If​ ​you​ ​need​ ​to​ ​do​ ​any​ ​transposition​ ​(octaves,​ ​semitones,​ ​cents),​ ​it​ ​should​ ​be​ ​done​ ​by​ ​adjusting​ ​the​ ​slider​ ​of​ ​the custom​ ​​v/o​​ ​control​ ​as​ ​there​ ​are​ ​multiple​ ​internal​ ​oscillators​ ​tuned​ ​by​ ​it. Evil​ ​twin​ ​contains​ ​a​ ​built​ ​in​ ​amplifier​ ​with​ ​a​ ​click​ ​reduction​ ​circuit.​ ​​ ​To​ ​set​ ​it​ ​up,​ ​go​ ​to​ ​the​ ​​gate​ ​in​ ​​custom​ ​control​ ​and assign​ ​it​ ​to​ ​your​ ​gate​ ​signal​ ​(G1-G4​ ​or​ ​A1-D4). The​ ​​gate​ ​in​​ ​control​ ​is​ ​pre-wired​ ​to​ ​trigger​ ​the​ ​envelope​ ​in​ ​the​ ​​env​ ​in​​ ​control.​ ​​ ​The​ ​​env​ ​in​​ ​has​ ​an​ ​ADSR​ ​envelope​ ​in​ ​it to​ ​get​ ​you​ ​started.​ ​​ ​You​ ​can​ ​adjust​ ​the​ ​ADSR​ ​parameters​ ​on​ ​the​ ​ADSR​ ​inside​ ​the​ ​​env​ ​in​​ ​control,​ ​or​ ​you​ ​can​ ​replace​ ​it with​ ​your​ ​own​ ​custom​ ​chain.

If you would like to use an external envelope/VCA, just adjust the env in slider to 1, and Evil Twin will output constant sound just like any other VCO.

Signal​ ​Flow

This​ ​unit​ ​contains​ ​two​ ​primary​ ​oscillators.​ ​​ ​The​ ​main​ ​oscillator,​ ​which​ ​is​ ​the​ ​oscillator​ ​you​ ​hear​ ​directly​ ​at​ ​the​ ​output, and​ ​the​ ​mod​ ​oscillator,​ ​which​ ​modulates​ ​the​ ​main​ ​oscillator​ ​in​ ​various​ ​ways​ ​(frequency​ ​modulation,​ ​phase modulation,​ ​and​ ​amplitude​ ​modulation)​ ​at​ ​audio​ ​rates.​ ​​ ​The​ ​general​ ​signal​ ​flow​ ​is​ ​that​ ​FM​ ​and​ ​PM​ ​are​ ​applied simultaneously​ ​and​ ​first,​ ​then​ ​AM,​ ​and​ ​finally​ ​the​ ​waveshaper​ ​is​ ​applied​ ​(if​ ​it​ ​is​ ​engaged).

EvilTwin SignalFlow.png


EvilTwin LocalControls.png

The​ ​controls​ ​can​ ​all​ ​be​ ​adjusted​ ​by​ ​pressing​ ​them​ ​and​ ​moving​ ​the​ ​encoder.​ ​​ ​But​ ​keep​ ​in​ ​mind​ ​that​ ​they​ ​are​ ​also​ ​all modular​ ​inputs!​ ​​ ​So​ ​they​ ​can​ ​receive​ ​signals​ ​from​ ​external​ ​modules​ ​or​ ​internal​ ​chains.​ ​​ ​A​ ​lot​ ​of​ ​creativity​ ​can​ ​be unleashed​ ​by​ ​CV​ ​controlling​ ​the​ ​various​ ​parameters.

Control Description
Red 1.png fm Controls​ ​the​ ​FM​ ​(frequency​ ​modulation)​ ​index​ ​or​ ​amount​ ​by​ ​which​ ​the​ ​mod oscillator​ ​modulates​ ​the​ ​main​ ​oscillator’s​ ​frequency.​ ​​ ​This​ ​is​ ​set​ ​up​ ​for​ ​linear through​ ​zero​ ​FM.
​Controlling​ ​this​ ​parameter​ ​over​ ​time​ ​by​ ​inserting​ ​an​ ​ADSR​ ​or​ ​other envelope​ ​generator​ ​into​ ​this​ ​chain,​ ​and​ ​triggering​ ​it​ ​with​ ​​gate​ ​in​​ ​is​ ​a technique​ ​frequently​ ​used​ ​in​ ​FM​ ​synthesis.​ ​​ ​Adjust​ ​the​ ​gain​ ​and​ ​offset​ ​of​ ​the envelope​ ​to​ ​taste.
Red 2.png pm Controls​ ​the​ ​PM​ ​(phase​ ​modulation)​ ​​ ​index​ ​or​ ​amount​ ​by​ ​which​ ​the​ ​mod oscillator​ ​modulates​ ​the​ ​main​ ​oscillator’s​ ​phase.
​​Just​ ​like​ ​the​ ​tip​ ​for​ ​fm,​ ​controlling​ ​this​ ​parameter​ ​over​ ​time​ ​by​ ​inserting an​ ​ADSR​ ​or​ ​other​ ​envelope​ ​generator​ ​into​ ​this​ ​chain,​ ​and​ ​triggering​ ​it​ ​with gate​ ​in​​ ​is​ ​a​ ​technique​ ​frequently​ ​used​ ​in​ ​PM​ ​synthesis.​ ​​ ​Adjust​ ​the​ ​gain​ ​and offset​ ​of​ ​the​ ​envelope​ ​to​ ​taste.
Red 3.png am Controls​ ​the​ ​AM​ ​(amplitude​ ​modulation)​ ​index​ ​or​ ​amount​ ​by​ ​which​ ​the​ ​mod oscillator​ ​modulates​ ​the​ ​main​ ​oscillator’s​ ​amplitude.​ ​​ ​Values​ ​up​ ​to​ ​1​ ​are amplitude​ ​modulation.​ ​​ ​Values​ ​above​ ​1​ ​veer​ ​into​ ​ring​ ​modulation,​ ​and​ ​the carrier​ ​signal​ ​begins​ ​to​ ​disappear,​ ​accentuating​ ​the​ ​sidebands.
Red 4.png quant When​ ​engaged,​ ​quantizes​ ​the​ ​frequency​ ​of​ ​the​ ​mod​ ​oscillator​ ​to​ ​1⁄2​ ​multiples (0.5,​ ​1.0,​ ​1.5,​ ​2.0,​ ​etc.)​ ​of​ ​the​ ​main​ ​oscillator’s​ ​frequency.​ ​​ ​This​ ​tends​ ​to produce​ ​melodic/harmonic​ ​sounds​ ​from​ ​AM,​ ​FM,​ ​and​ ​PM.​ ​​ ​When​ ​in​ ​the​ ​off position,​ ​the​ ​ratio​ ​is​ ​free,​ ​which​ ​can​ ​produce​ ​inharmonic/clangorous​ ​sounds.
Red 5.png ratio The​ ​ratio​ ​of​ ​the​ ​frequency​ ​of​ ​the​ ​mod​ ​oscillator​ ​to​ ​the​ ​main​ ​oscillator.​ ​​ ​See also​ ​Quant​ ​above.
​​In​ ​traditional​ ​FM​ ​and​ ​PM​ ​synthesis,​ ​this​ ​parameter​ ​is​ ​typically​ ​not modulated​ ​over​ ​time,​ ​but​ ​fixed.​ ​​ ​You​ ​might​ ​want​ ​to​ ​connect​ ​this​ ​parameter​ ​to an​ ​external​ ​offset​ ​for​ ​ease​ ​of​ ​adjustment​ ​while​ ​designing​ ​sounds.
Red 6.png fb main Feeds​ ​the​ ​main​ ​oscillator​ ​back​ ​into​ ​its​ ​frequency​ ​control.​ ​​ ​This​ ​results​ ​in morphing​ ​of​ ​the​ ​oscillator’s​ ​waveshape​ ​from​ ​a​ ​sinusoid​ ​at​ ​zero​ ​to​ ​a​ ​ramp​ ​at max.
Red 7.png fb mod Feeds​ ​the​ ​mod​ ​oscillator​ ​back​ ​into​ ​its​ ​frequency​ ​control.​ ​​ ​This​ ​results​ ​in morphing​ ​of​ ​the​ ​oscillator’s​ ​waveshape​ ​from​ ​a​ ​sinusoid​ ​at​ ​zero​ ​to​ ​a​ ​ramp​ ​at max.
Red 8.png fold Engages​ ​a​ ​sinusoidal​ ​wavefolder.​ ​​ ​This​ ​results​ ​in​ ​distortion​ ​of​ ​the​ ​sound.​ ​​ ​If you​ ​engage​ ​this​ ​when​ ​the​ ​​fld​ ​gn​​ ​control​ ​is​ ​set​ ​to​ ​zero,​ ​you​ ​will​ ​hear​ ​no sound,​ ​and​ ​will​ ​need​ ​to​ ​turn​ ​up​ ​​fld​ ​gn​ ​​to​ ​taste.
Red 9.png fold gn Adjusts​ ​the​ ​amount​ ​of​ ​gain​ ​into​ ​the​ ​wavefolder.​ ​​ ​Higher​ ​values​ ​increase distortion.
Red 10.png f shift Produces​ ​an​ ​asymmetry​ ​in​ ​the​ ​wavefolder,​ ​altering​ ​the​ ​timbre​ ​of​ ​the distortion.
Green 11.png v/o Connect​ ​your​ ​v/o​ ​input​ ​to​ ​this​ ​control​ ​to​ ​control​ ​the​ ​pitch.​ ​​ ​You​ ​can​ ​also​ ​do transposition/tuning​ ​with​ ​this​ ​control.
Green 12.png gate in Master​ ​gate​ ​control​ ​for​ ​the​ ​unit.​ ​​ ​Connect​ ​your​ ​gate​ ​signal​ ​here.
Green 13.png env in This​ ​control​ ​contains​ ​a​ ​built​ ​in​ ​envelope,​ ​and​ ​is​ ​pre-wired​ ​to​ ​be​ ​triggered​ ​by gate​ ​in​.​ ​​ ​By​ ​delving​ ​inside​ ​this​ ​control,​ ​you​ ​can​ ​adjust​ ​the​ ​attack,​ ​decay, sustain,​ ​and​ ​release​ ​parameters,​ ​which​ ​are​ ​applied​ ​to​ ​the​ ​amplitude​ ​of​ ​the final​ ​signal.

You​ ​can​ ​also​ ​replace​ ​the​ ​chain​ ​inside​ ​this​ ​with​ ​one​ ​of​ ​your​ ​own​ ​design.​ ​​ ​If you​ ​wish​ ​to​ ​use​ ​an​ ​external​ ​gate/envelope​ ​from​ ​an​ ​outside​ ​modules,​ ​just delete​ ​the​ ​chain​ ​inside​ ​of​ ​this​ ​control,​ ​and​ ​specify​ ​the​ ​input​ ​(G1-G4​ ​or​ ​A1-D4) of​ ​your​ ​incoming​ ​envelope.

Blue 14.png mod in Connect​ ​an​ ​input​ ​here​ ​to​ ​modulate​ ​the​ ​modulation​ ​oscillator’s​ ​frequency​ ​or phase.​ ​​ ​Using​ ​this,​ ​you​ ​can​ ​build​ ​FM/PM​ ​algorithms​ ​that​ ​have​ ​more​ ​than​ ​two operators.
Blue 15.png mod amt Controls​ ​the​ ​gain​ ​of​ ​the​ ​​Mod​ ​In​​ ​input​ ​to​ ​the​ ​modulation​ ​oscillator’s​ ​frequency or​ ​phase.
Blue 16.png fm/pm Controls​ ​whether​ ​​Mod​ ​In​​ ​is​ ​routed​ ​to​ ​the​ ​modulation​ ​oscillator’s​ ​frequency​ ​or phase.​ ​(Toggle​ ​off​ ​for​ ​FM,​ ​on​ ​for​ ​PM).
Orange 17.png main This​ ​control​ ​contains​ ​the​ ​main​ ​oscillator.​ ​​ ​You​ ​do​ ​not​ ​need​ ​to​ ​adjust​ ​this control​ ​or​ ​delve​ ​into​ ​the​ ​chains​ ​inside​ ​of​ ​it​ ​unless​ ​you​ ​want​ ​to​ ​further customize​ ​this​ ​unit.
Orange 18.png mod This​ ​control​ ​contains​ ​the​ ​mod​ ​oscillator.​ ​​ ​You​ ​do​ ​not​ ​need​ ​to​ ​adjust​ ​this control​ ​or​ ​delve​ ​into​ ​the​ ​chains​ ​inside​ ​of​ ​it​ ​unless​ ​you​ ​want​ ​to​ ​further customize​ ​this​ ​unit.

Building​ ​FM/PM​ ​Algorithms

The​ ​unit​ ​is​ ​a​ ​self​ ​contained​ ​two​ ​operator​ ​FM/PM​ ​oscillator.​ ​​ ​You​ ​can​ ​build​ ​more​ ​complex​ ​algorithms​ ​by​ ​using​ ​multiple instances​ ​of​ ​this​ ​custom​ ​unit. To​ ​add​ ​another​ ​carrier,​ ​place​ ​two​ ​units​ ​in​ ​a​ ​chain,​ ​each​ ​inside​ ​a​ ​mixer. To​ ​add​ ​additional​ ​modulators,​ ​you​ ​can​ ​specify​ ​this​ ​custom​ ​unit​ ​as​ ​the​ ​input​ ​on​ ​the​ ​​mod​ ​In​​ ​of​ ​another​ ​unit.

CPU​ ​Usage

This​ ​unit​ ​uses​ ​roughly​ ​18%​ ​of​ ​CPU​ ​for​ ​each​ ​instance.​ ​​ ​If​ ​you​ ​need​ ​to​ ​reduce​ ​the​ ​CPU​ ​usage​ ​and​ ​don’t​ ​need​ ​the wavefolder​ ​functionality,​ ​first​ ​turn​ ​the​ ​wavefolder​ ​off.​ ​​ ​Then​ ​go​ ​to​ ​Admin-->Settings-->General​ ​and​ ​make​ ​sure​ ​“Does bypassing​ ​a​ ​unit​ ​also​ ​disable​ ​it?”​ ​is​ ​set​ ​to​ ​yes. Navigate​ ​into​ ​the​ ​custom​ ​unit​ ​by​ ​selecting​ ​“open”.​ ​​ ​Click​ ​on​ ​the​ ​mixer​ ​unit​ ​called​ ​“foldMix”​ ​and​ ​bypass​ ​it.​ ​​ ​This​ ​will reduce​ ​CPU​ ​usage​ ​to​ ​around​ ​13%​ ​for​ ​that​ ​instance​ ​of​ ​the​ ​unit.