While this side of the market has become saturated, flagship, polyphonic designs with voltage-controlled oscillators (VCOs) remain relatively underserved. As many analogue purists would be happy to tell you, VCO-based synths tend to outperform their digitally-controlled counterparts in the area that matters most: sound. Building polyphonic synths without digital control of the oscillators has traditionally been an expensive and complex undertaking, which explains why you see far fewer of these being released.
So it was something of a surprise when Korg announced the new Prologue line of synths at this year's NAMM conference. They designed two versions, a 49-key eight-voice unit called Prologue 8 and a 61-key version with double the voices named Prologue 16. We were able to get our hands on a Prologue 16 for our tests, so this review will be based primarily on that model. There are some fairly important differences however, which we'll touch on.
The core of the Prologue voice architecture is similar to Korg's well-traveled minilogue and monologue synths. You get two VCOs with sawtooth, triangle and square wave shapes with a four-octave switch. There's also the ability to enable ring modulation, sync and cross modulation between the two. With the Prologue, Korg added a third digital oscillator to the mix. Despite straying from the analogue path, it ends up being one of the instrument's best features. It's really like getting three oscillators in one, as it gives you the option to switch between three modes, each with different timbral choices. There's a noise mode with four types of noise, a variable phase modulation (VPM) mode with 16 types to choose from and a user oscillator that will eventually allow you to load your own bespoke waveshapes via a future update.
The VPM oscillator is the star of the show here. It actually houses a pair of internal oscillators capable of frequency modulation, allowing you to layer complex timbres on to the already-excellent VCOs. Korg includes a diverse set of waveshape combinations selectable with the Type knob, while the Shape knob allows you to dial in the modulation amount as well as the ratio. There are some other very useful VPM engine parameters (like envelope control of the mod amount) but they're unfortunately hidden in the Prologue's edit mode menus. As such, they're only controllable using the indented Program/Value encoder, which is less than ideal. The fact that these also aren't controllable via MIDI was even more discouraging. But the digital architecture means it's possible to change this in the future.
The Prologue's signal then passes through a two-pole lowpass filter with drive, keytracking and low cut options. The drive and low cut features are very nice to have here, but having them controlled by rocker switches was an odd choice—I'd prefer to have finer control over both parameters. As one would expect, there's a standard ADSR envelope for both the filter and the amp. The former can also control the pitch of the oscillators. After passing through the amp, the signal hits a digital effect section. There are two slots to work with. One offers a selection of modulation effects including multiple flavours of chorus, ensemble, phaser and flanger, while the other lets you choose from a dozen types of reverb. Finally, the Prologue 16 has one last exclusive trick up its sleeve that its little brother lacks: the LF Comp, a low-end booster/compressor that uses an analogue circuit to add a bit of bottom-end warmth.
If the LF Comp doesn't convince you that the Prologue 16 is the better choice, the dedicated controls for Korg's sub timbre program could be the deciding factor. This is one of the best features of the Prologue, as it gives you the ability to load two programs at once and play and control them simultaneously. There are three play modes to choose from that allow you to either layer the programs, crossfade them as you play up the keyboard or split the keyboard and play them separately. The Prologue 16 has dedicated controls for all of this, including a knob to set the balance between the two programs. As a result, I found myself using this feature constantly, which would likely not be the case with the menu diving required on the Prologue 8. But even with all the dedicated controls, I still found myself doing more menu navigation than I would have liked. The process is made more complex by the unlabelled edit buttons.
Overall, I was impressed with what Korg achieved on the Prologue. The sound is undoubtedly thick and impressive. With 16 voices to work with, the layering features and digital effects, there's a huge range of excellent, playable sounds. The future is bright as well, as end-users will soon be able to load custom waveshapes and effects developed using Korg's Software Development Kit. As an expensive flagship instrument, though, it's not ideal for everyone. In addition to the negatives I've already mentioned, the modulation capabilities are underwhelming. There's only one LFO, no aftertouch, and—perhaps the most perplexing omission—no sign of the minilogue's sequencer/motion recorder. This last feature alone would be a huge benefit to the Prologue. Hopefully Korg has plans to add it via a future firmware update.
Ease of use: 3.7