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Get DirtBoxSynth Custom Oscillator Pack FREE with the Korg Prologue

Posted on August 10, 2018 by Richard Bottom There have been 0 comments



The Korg Prologue is unique in that it's a flagship analogue synth with an open-source digital oscillator and effects section available for developers to add their own sounds. The first 3rd party oscillators have been release by DirtBoxSynth and sound very interesting!


We wrote this article about what's involved in getting the Prologue SDK up and running a little while ago, and since then a 3rd party - DirtBoxSynth - has taken up the baton and produced an oscillator pack for the Prologue - 'FMonsta'. For a limited time, if you buy a Prologue 8 or Prologue 16 from Absolute Music you can get FMonsta FREE!

There are two oscillators included in the pack - FMonsta and FMonsta2. Both oscillators use hybrid wavetable/FM algorithms, and offer different sounds to the standard Prologue Multi Engine oscillators. FMonsta is gnarly, twisty, turny, and harmonic-rich – great for leads and basses and general gritty FM mayhem. By contrast, FMonsta2 is a softer oscillator that can modulate between straight and FM combinations of the waves, with an additional LFO and modulated distortion. FMonsta 2 lends itself more to pads and evolving textures with this additional modulation.



The FMonsta oscillator creates harmonically complex timbres by using both wavetable and frequency modulation synthesis 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 SHAPE control as a second modulation source. This is accessed by holding SHIFT and turning SHAPE to set the modulation amount.

The controls are:


  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

In use this thing screams! The SHAPE control offers a real hands-on performance control that sweeps through the harmonics as the FM wave changes pitch. Here's an example from the developer of how this can sound..


FMonsta 2 takes the same wavetables as FMonsta but combines and presents them in a different way. The SHAPE control still affects the pitch of wave B whilst it's interacting with wave A, which can of course be modulated by the main Prologue LFO, but it is much more gentle sounding.

SHIFT SHAPE mixes from added waves to multiplied waves and can be modulated with an additional LFO (parameter 6).

Distortion can be applied to the oscillator, and the additional LFO can also be assigned to the amount of distortion. 

This oscillator is much smoother and with the multiple modulation options is great for pads that evolve naturally, the SHAPE control is much more subtle but in combination with SHIFT_SHAPE sets the harmonic profile.

As with FMonsta, combining different can produce very different results - and there are hundreds of combinations!


  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  

The FMonsta oscillators are loaded into our demo Prologue in store, so if you are in the area be sure to check them out!

If you wish to purchase the FMonsta Oscillator Pack, or download the free Prologue Panner, then head over to the DrtBoxSynth website.

This post was posted in Blog entries, Current News, Keyboards & Synths, New Releases, Product News, Product Previews and was tagged with Korg, oscillator, prologue, sdk, synth, synthesizer