A polysynth with up to 16 voices and a sound all its own

When it comes to synths, Korg has really carved out its own niche in the past decade. The company seems to understand what musicians want; a playable synth with analog sound quality (and some digital features for convenience) that is affordable and fits particular musical concepts. For example, the lowest note on the Monologue is an E, which makes that mono-synth perfect for playing basslines in a band with guitars and basses (which have a low-E string). The Minilogue, on the other hand, is a 4-voice analog synth for the desktop with velocity-sensitive keys that is priced just under $500. And it sounds really great!

Consequently, many have already been predicting what Korg’s next step would be in its “-logue” line. As usual, the company went further than expected.

With the Prologue, Korg didn’t simply increase the voice count of a previous model: It added significant features that allow the instrument to create sounds its previous synths could not achieve. Even within the most basic patches, the Prologue’s hybrid analog/digital architecture has a sound all its own that, surprisingly, leans as much towards aggressive timbres as it does mellow analog-like tones.

A couple of weeks ago, Korg sent us a Prologue for review, and here’s what we found.

What’s in a Voice

The dual-timbral Prologue is available in 8-voice ($1,499) and 16-voice ($1,999) versions, with 49 and 61 keys, respectively. (We tested an 8-voice model.) At its most basic level, the signal path for each voice sends three sound sources through a mixer, then through an analog VCF and VCA before hitting the effects and master output. Each voice also includes an LFO that can control the VCOs or VCF, and a pair of 4-stage envelope generators; one for controlling the VCOs and filter and the other for the VCA. (The LFO and EGs are digital).

Each voice includes two analog oscillators that utilize the same design as Korg’s other “-logue” models. There are three wave shapes to choose from on each (saw, triangle, square), on octave switch, and knobs for setting the Pitch and for altering the waveforms. You can also introduce hard sync, ring modulation and cross modulation between the two oscillators.

In addition, each voice includes a digital oscillator, the Multi Engine, where you can select an FM-like VPM (variable phase modulation) waveform, one of three kinds of noise, or any sound you’ve added yourself—very cool. Another noteworthy aspect of the Multi Engine is that it can be placed before or after the filter. For example, you could setup a patch where the analog oscillators are filtered but the digital waveform is not.

The Prologue has four voice modes—Poly, Mono, Unison, and Chord—with two controls. Voice Mode Depth is used for determining the voice behavior. For example, in Chord mode it’s used for selecting the chord type, whereas in Mono mode, you can set it so that low-octave sounds come in first. With the Voice Spread knob, you can determine where each voice appears in the stereo field based on the mode. My favorite is in Poly mode, where the voices are randomly panned as you play.

If you want to use two timbres simultaneously as you play, push the Sub On button. This mode divides the voice count in half between the two sounds, but now you can use the Main/Sub knob to crossfade between the two timbres, as well as setup layers and splits on the keyboard.

Oh, That OTA Filter

Much of the Prologue’s character comes from its resonant, 2-pole (12dB/octave) OTA filter. It’s a new circuit design that was chosen for its interesting timbral qualities, which the designer says is in some part due to nonlinearities in its feedback chain. In fact, the filter sounds particularly good on the Multi Engine oscillator. And, as you dial in resonance, the signal stays strong and perky throughout. A 3-position switch for keyboard tracking is provided.

The Prologue’s filter includes two additional tone-shaping controls. The first is a switchable highpass filter with a cutoff frequency of roughly 500 Hz (6dB/octave). I found this to be useful for reducing the low-end when playing chords in a dense mix. The second is the analog drive circuit, which has three settings: off, 50%, 100%. This allows you to beef up the sound of each voice in your patch. And if that’s not enough, the Prologue has a low-frequency compressor (with variable input gain) on the main output, which can be switched on to push the signal even harder.

At this point in the signal flow, the Prologue is already capable of creating an up-front, modern sound when you need it, though it can also be quite mellow.

Dual Digital Effects

Next, the Prologue sends its voices through a modulation effects block, followed by a Delay/Reverb effect. Rather than provide a single type for each effect as the Minilogue does with its delay, the Prologue gives you several options under each category. The chorus types include Stereo, Light, Deep, Triphase, Harmonic, Mono, Feedback, and Vibrato. Speed and Depth controls allow you to adjust the effect to taste.

The Delay and Reverb options include common programs such as Early Reflection, Room, Hall, and Arena, as well as effects with much more personality like Submarine, Horror, Space or Riser. The later ones add pitch and modulation to the effect to further enhance the rhythm and texture of what you’re playing.

Speaking of rhythm, the Prologue includes a basic arpeggiator, and you can set it differently for either timbre when you’ve split the voices. You can tap in the tempo, set the range (from 1 to 4 octaves) and choose one of five types of arpeggio (order played, up, down, up/down, and random).


It doesn’t take long to realize that the Prologue is a very simple and straightforward synth to program and play. The stuff you need for sound design or for setting up performance parameters is right there in front of you. And when you come up with something you want to save, the process is easy.

For me, this is at the heart of what Korg is trying to get across with the “-logue” part of its name: It’s a reference (by way of the English spelling of analog) to the early days of synthesizers when every parameter was immediately at your fingertips. Now, of course, we have the ability to save and recall our settings, giving us instant access to whatever sounds we need for a gig. Oh, and we also have onboard digital effects, an arpeggiator, MIDI, USB, and all the modern conveniences we’ve come to expect in a performance-oriented keyboard.

Of course, the Prologue’s name is also meant as a reference to the instrument’s sound, which was described to me as “analog sound” with “digital assistance.” Well, this synth does have a digital sound source, so there goes that bit of marketing.

Essentially, the Prologue a hybrid synth. And it’s 2018, so that shouldn’t surprise or bother anyone. (If it does, Korg has fully analog instruments to check out.)

However, the Prologue doesn’t have all the bells and whistles you might imagine in a polysynth, but instead strikes a useful balance of features that are easy to reach and remember. And the instrument, overall, is relatively small, lightweight, and inexpensive for what you get.

But what the Prologue does have is a distinctive sound, which is what many of us look for in a synthesizer. The factory patches cover all the requisite instrument types and give you a good idea of the synth’s capabilities. Its sound palette ranges from smooth to aggressive, making it suitable for old-school playing or use in modern genres.

Overall, the Prologue delivers what you would expect from this line of Korg synthesizers (and a number of things you didn’t expect) in an instrument that is as fun to play as it is to hear.

For more information, visit korg.com.