DirtBoxSynth Released FMonsta Custom Oscillator Pack For The KORG Prologue Synthesizer!

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FMonsta by DirtBoxSynth is a custom FM oscillator pack for the KORG Prologue Synthesizer that lets awake its powerful customizable multi-engine.

At the NAMM 2018, the new KORG Prologue hardware analog poly Synthesizer was introduced with big anticipation. Many were disappointed because the instrument has only one LFO or no sequencer on board. For me personal, the most exciting point of it is the user-definable digital multi-engine with which you can do a lot.

Now after a few months on the market, the first third-party company has developed a new oscillator section for the multi-engine using the SDK. FMonsta is an oscillator pack that is based around wavetable and phase/frequency modulation techniques. Each pack features a selection of parameters that gives you freedom to play around with the new engine.

Per example: the FMonst has a loopable envelope while FMonst 2 includes an internal LFO and distortion. With these packs, you can easily expand the sound range of the Prologue Synthesizer. Hopefully it’s just the beginning of several new oscillator and effects engine.


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


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

Beside this the developer also released a free ModFX expansion for all KORG Prologue Synthesizer user. The DirtBoxSynth Classic Panner is a basic autopan effect for the custom Mod Effect user slot.

The FMonsta Pack (1 & 2) is available now for £20 on the DirtBoxSynth website. The developer will require the Prologue serial number to enable to deliver the customer oscillator engine. The AutoPanner for the ModFX is available for free for all Prologue customer.

More information here: DirtBoxSynth

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