Custom Oscillators for the Prologue

The Prologue is a true analogue synth but also has a digital oscillator section that can add harmonically rich and interesting timbres. When Korg announced that they would open up the digital side of  their flagship synth to developers to create custom code for the Multi Engine, we understandably got a bit excited. Although our own hardware is yet to be released, we felt that this was a great opportunity to get some of the DirtBoxSynth algorithms out into the wild. 


Classic fat pads and leads with added PWM

DirtBoxSynth SUPAwave is a 7-voice per note oscillator that incorporates the classic note ‘spread’ effect that creates rich, thick, de-tuned sounds that are great for huge pad and leads. 

As well as the classic ‘super variety’ saw wave , SupaWave can ‘spread’ other waveforms including square and also pairs of waveforms that can be swept or modulated for PWM/Phasing-type effects between the two half-waves. SUPAwave also throws an extra LFO and distortion into the mix for added colour and movement.

When in advanced modes, the SHAPE control no longer controls the amount of ‘spread’, but changes the point in the waveform cycle at which the second wave is heard. By sweeping the Shape control (or applying LFO modulation via either LFO), the Width of one wave relative to the other is varied to allow PWM-type changes that tend to create phase sweeps when the detuned voices are louder, and are more like classic PWM when the voices are less detuned or mixed down. In advanced modes, the Spread amount can still be accessed via the menu parameters. Randomness of the initial voice phases can be set using Shift_Shape. 

The basic and advanced waveforms are selected with Wave Type as follows:

Basic Modes:

1.       Saw

2.       Square

Advanced Modes:

3         Square/inverted Saw

4         Parabolic /Inverted Square

5         Parabolic /Inverted Saw

6         Square / Inverted Parabolic

7         Parabolic / Inverted Parabolic

8         Square / Inverted Square

Customer demo of SUPAwave by Ron Cavagnaro


1.       Supa Mix - controls the level of the six detuned voices relative to the main voice.

2.       WaveType – selects the basic or advanced PWM-enabled waveform (see Basic and Advanced modes section)

3.       Distortion Amount - sets the amount of ‘soft clipping’ on the signal

4.       Spread – spreads the pitch of the detuned oscillators (the same as Shape in basic modes)

5.       LFO Amt – sets the amount of Multi Engine LFO to Shape (PWM point for advanced waves)

6.       LFO Rate – sets the speed of the Multi Engine LFO

Shape:  Spread (in basic mode) / PWM control (with dual waves)

Shift_Shape: Controls the amount of phase randomness


Custom Oscillator Pack for the Prologue Synthesizer

FMonsta is an oscillator pack for the Prologue including FMonst and FMonst2. Fmonst is great for cutting leads, basses and sequences, whereas FMonsta2 is softer and suits more evolving textures and introduces more subtle harmonics. FMonst has a loopable envelope while FMonst 2 includes an internal LFO and distortion, and both are based around wavetable and phase/frequency modulation techniques.



FMonsta1 creates harmonically rich timbres by using both wavetable and frequency modulation techniques. Two waveforms are combined additively or by multiplication (depending on the mode chosen) creating hundreds of possible spectral waves. The SHAPE control determines the frequency of the modulating waveform and opens up many performance possibilities.

A simple envelope with attack and decay also affects the FM algorithm with the Envelope Amount control determining the modulation amount.  This envelope can be set to loop so as to create a symmetrical or asymmetrical LFO which modulates the FMonsta oscillator independently of the main Prologue LFO. The main Prologue LFO can also be assigned to the FM algorithm as a second modulation source. This is accessed by holding SHIFT and turning SHAPE to set the modulation amount.



  1. Oscillator wave
  2. FM Wave
  3. Envelope Amount
  4. Attack
  5. Decay
  6. Mode / Algorithm
  7. SHAPE:     FM Pitch Centre
  8. SHIFT_SHAPE:  logue LFO to Shape Mod  

Envelope Modes

  1. Algorithm A - single shot
  2.  Algorithm B - single shot
  3.  Algorithm A - looping
  4. Algorithm B - looping

FMonsta2  (version A and B)

Softer than FMonsta, FMonsta2 uses the same hybrid engine, but with different controls and sound, and two performance variations The distortion adds colour while the dedicated LFO allows modulation of the FMmix and/or the distortion amount.

In version A, SHAPE sweeps the second oscillators pitch while SHIFT SHAPE mixes from added waves to multiplied waves and can be modulated with an additional LFO. The LFO can also be assigned to the amount of distortion. SHAPE affects the pitch of wave B whilst interacting with wave A.



  1. Wave A
  2. Wave B
  3. Distortion Amount
  4. Extra LFO - to Distortion
  5. Extra LFO - rate
  6. Extra LFO - to FM morphing
  • SHAPE:     FM Pitch Centre
  • SHIFT_SHAPE:  logue LFO to Shape Mod 

  note: VERSION B swaps these last two controls

If you would like to purchase an FMonsta licence for your Prologue, please use the Paypal link here and wait for an email. We will require your Prologue serial number to enable us to deliver your Custom Oscillator.

Video Demos of FMonsta Oscillators

Short demo of FMonsta1 by DirtBoxSynth

Demo of FMonsta1 by Ron Cavagnaro

FMonsta2 demo - thanks again to Ron!

Audio Demos of FMonsta

FMonsta Audio Demo:

Running through some wave combinations of FMonsta.. In this example different wave combinations are swept manually by the SHAPE control:

FMonsta 2 Audio Demo

This example demonstrates the use of the additional LFO set to modulate the distortion and FMmix amounts.


The Organ with a Twist!

ORGANism Custom Oscillator for the Korg Prologue

ORGANism recreates the sound of an organ but with a twist. The six editable parameters control the level of each ‘partial’ like drawbars, and Shift_Shape changes the organ voicing - giving the different tones and harmonics that produce different organ sounds that can then be further sculpted with the drawbar volumes (parameters 1-6).

The Shape control, on the other hand, is not a conventional organ control! It changes the pitch of each partial differently so that when fully clockwise produces a different inversion of the organ harmonies. Some go up to related frequencies, while others will simultaneously go down, allowing for interesting performance possibilities. When this control is used just off minimum, a very natural 'chorus' is produced.

Used in conjunction with the DirtBoxSynth Prologue Panner or other MOD FX, both classic and unconventional organ sounds can be produced.

So what do our customers do with ORGANism?

 Check out this great demo by Ron Cavagnaro...

A short demo of some of the sounds coming from ORGANism -

DirtBoxSynth Oscillator Bundle

For a limited time only, get all current DirtBox Prologue oscillators as a bundle for only £40 - Includes FMonsta Pack, ORGANism and SUPAwave.

If you have already purchased any DirtBoxSynth oscillators and would like to take advantage of this offer, please get in touch via email.

If you are interested in knowing a bit more about the Kork Prologue SDK that allows anyone with the appropriate skill-set to create their own oscillators and effects, then check out this article written for Absolute Music.

Prologue Custom Effects

Basic AutoPanner (ModFX)

FREE for all Prologue owners... the DirtBoxSynth Classic Panner - a basic autopan effect for the custom Mod Effect user slots on the Korg Prologue 8 and Prologue 16.

 Speed and depth basically do what you might expect ;)  Enjoy!

AMPit - Hi-Gain Distortion (MOD FX)

AMPit is a hi-gain distortion plug-in for Prologue MOD FX.

Control 1 (usually Speed) sets the amount of gain going into the distortion algorithm, and Control 2 (Depth) is a tone control.

As the Mod Wheel can be assigned to Control 1 (Speed), the amount of distortion can be controlled easily during a performance.

The tone control is great for knocking back some of the harmonics created by the distortion if required, keeping the main Prologue filter as part of the synth patch.

Filter Pack for the Prologue

This pack is a set of resonant second order filters for the MOD FX section of the Prologue.

There are four filters – low pass, high pass, band pass and band reject.

Each filter has the same controls:

Control1 (Speed) sets the frequency of the filter, and can also be modulated with the Mod wheel.

Control 2 (Depth) controls the amount of resonance of the filter.