The Big Review: Korg Opsix

For all its appeal, Yamaha’s DX7 proved a programming nightmare for many. Can Korg repurpose FM synthesis and make it accessible for a new generation?

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Korg Opsix

Price £599
Contact Korg

Of the many consumer-facing and industry-changing technological battles that have been fought over the years, some have had clear winners that have set new standards against which their rivals are judged. Synthesisers have seen their fair share of competition down the decades, not solely in terms of manufacturers competing with what they’re able to pack into their instruments but via the foundations of the very sounds they produce.

In terms of popularity, by this point it’s pretty clear that subtractive synthesis has won out. Most synth users are familiar with oscillators that feature waveforms that are blended together before being passed through filters and amps, with LFOs and envelopes there to help shape each of those stages via modulation. Yet subtractive synthesis is by no means the only way in which synthesised sounds can be generated. Yamaha’s DX7, one of the world’s most famous synths and still considered a landmark instrument today, is veritable proof of this.

The DX7 relies on FM (frequency modulation)synthesis, plotting an alternative pathway to electronic-sound generation. The problem with the DX7 was that its algorithmic approach and use of waveforms not as sonic builders in their own right but as modulation sources seemed baffling to many users. It’s perhaps true that its approach to sound design appealed more to programmers than to traditional musicians.

Yet the DX7s hall-of-fame status has never dimmed. For many years, manufacturers have tried to find ways to facilitate the capabilities of FM without confusing new generations of potential users. Here, Korg attempts to put FM back on the sound-generating map with its new synth, the Opsix.

Korg Opsix

Green machine

The Opsix’s design follows in the footsteps of the Wavestate, another recent synth designed to facilitate the occasionally confounding workflow of its inspiration. The Wavestate is modelled on an original Korg design, the Wavestation.

But there’s a new format of synthesiser that Korg has identified through this pair of instruments, which makes you wonder what else their engineers have planned for the future. The Opsix is one of the most square keyboards we’ve ever played. It’s only three octaves wide and there’s a deep and generous panel of dials and switches above its keybed that makes the synth feel almost as broad as it is long – and appealingly chunky to boot.

The rear panel has a headphone out, stereo outs, a USB port, five-pin MIDI in/out ports and an inlet for the power supply. The power button is located here too. Press it and the Opsix lights up, its shining backlit rotaries and sliders dominating the left side of the panel. There’s also a series of stepped lights for the onboard sequencer running above the keybed at the bottom, and a set of six rotaries flanked by operational buttons that dominate the middle and right sides. The central section is anchored by an OLED display that acts as the nerve centre for programming the Opsix. It also provides users with a Minilogue-style oscilloscope if you press the Analyzer button.

Korg Opsix

Let’s get algorithmic

The reason subtractive synthesis makes sense to the vast majority of synth users is the same reason that making models from clay makes sense to children: you begin with a block of material and whittle away at it until it resembles the shape or character you want, at which point you’ve done it. With subtractive synthesis, that block is a combination of waveforms blended at the oscillator stage, before you’re able to use parameters to chip away and fashion it into a sound with the tone, volume, shape, wobble, vibrato and presence you want.

At the heart of FM synthesis lies an altogether different approach, more to do with carriers and modulators than with clay and craft knives. Think of a carrier as a regular oscillator; it’s the modulators here that tend to confuse programmers of FM synths. These are oscillators too but, rather than being patched to an output so that they can be heard, they are instead ‘interrupters’, signals designed to modulate the frequency and harmonics of a carrier to warp its shape into something new.

Traditional FM synthesis isn’t the only approach you can use to shape the Opsix’s sounds

Still with us? Things get more complicated from here. There are a number of algorithms available in FM synths that determine which of its sound sources are carriers and which are modulators. For instance, using one algorithmic structure, you might have five carriers whose combined output can be warped by a single modulator. In another, perhaps the modulator only interrupts the output signal of carriers four and five but not carrier signals one, two and three.

Korg Opsix

With the Opsix, Korg simplifies this mystifying process and presents it to users without overwhelming them. There are six operators here, each of which can act as a carrier or a modulator. Once you have scanned the presets to get a sense of what the synth can do, you’ll be ready to go. To make sounds of your own using the Opsix, you’ll first need to select an algorithm (or structure). This is done by pressing the Algo button on the top panel, before using the first rotary dial to scroll through the options. Not only will the OLED display show you a small graphic for each algorithm, you’ll also see the lights for the rotaries and sliders on the left change colour to indicate whether it’s a carrier (red/pink) or modulator (blue/purple).

In the display, each operator is represented by a die, with its number indicating its place in the overall structure. Once you’ve loaded an algorithm you like, you can then start to mix those elements. The sliders for the carriers turn their volume up and down (remember, these make a noise), while the rotaries above tune them in octaves. Push a modulator’s slider up and the amount of modulation it provides will increase. So while these don’t make a noise in the same way, the effect they have on a carrier becomes more intense as they are pushed higher. Similarly, their rotaries control frequency too – by rotating to the right, frequencies multiply to produce faster and more intense modulations.

Korg Opsix

Call the operator

Using the operator buttons below the rotaries, you can jump directly to the function you want to edit, before using the OP Select buttons (+ or -) to highlight what you want to work on. Here, the Opsix truly comes alive and you begin to realise that Korg has dragged FM synthesis kicking and screaming into the 21st century. Traditional FM synthesis as outlined above, you see, isn’t the only approach you can use to shape sounds. In fact, in the Opsix, it’s but one of five modes, all of which make use of related but distinct approaches to sound creation.

The first of these modes is DX-style traditional FM, which you can select by using the first of the six rotaries (labelled A) to scroll between it and other modes. Having chosen a mode, you can pick its waveform via the dial below. One of the major plus points about the Opsix is that you can audition and hear options without having to commit to them. This frees you up to scroll through and listen to the choices available but only make changes when you can confirm you like one more than another. It’s not exactly a shout-it-from-the-rooftops addition but is the kind of quiet quality-of-life feature that could really warm the synth to your workflow.

For each of the modes you can select here, the remaining rotaries are assigned to related parameters. In the FM mode, for example, there are dials for feedback and width. The other modes are Ring Modulation, Filter, Filter FM and Wave Folder, each of which alters the behaviour of the selected waveform. Remember, each of these can be a carrier or a modulator and, as each operator therefore becomes a malleable combination of harmonics (or a pure sine wave), its power in either category can be thrillingly diverse as a result of these interchangeable modes.

Korg Opsix

Taking shape

Once you’ve got your head around the shape, behaviour and harmonic footprint for each operator, further functionality allows you to warp sounds to taste in a series of ways. Buttons to the right of the Mode switch let you control key functions, the first of which is the Pitch button. Pitch can either be manipulated in a fixed, traditional way or via a ratio, which effectively multiplies or divides the frequency of the wave.

You can also detune things to add enormous amounts of richness to sounds. Next comes a Level/EG button that lets you shape both the overall level, as well your attack, decay, sustain and release phases and, via a second press of either of these buttons, you can dive into deeper pages that control LFO and further envelope assignments. Under the Modulators button, you can cycle through functionalities for three envelope generators and three LFOs, some of which are tied to specific areas of the synth engine (pitch or filter stages, for example) and some of which you can freely assign.

The multimode filter offers several curves with low-pass, high-pass and band-pass designs, including a modelled MS-20-style low-pass filter, with resonance available for any filter choice you make. The Effect button provides access to three onboard effects engines (press multiple times to cycle between parameter pages for each) with a long list of available effects per engine, including everything from doubling effects such as chorus, phaser and flanger to crunchy distortions and guitar-amp simulations and even spatial effects like delays and reverbs. Again, the rotary dials pick key parameters from each effect type for you to tweak.

Korg Opsix

The gate keeper

The Opsix’s arpeggiator is one of the best ways to experiment with the structure of its sounds and begin exploring the carriers and modulators. Once you’ve enabled it and held down a chord, you’ll find that pushing the sliders up and down to alter the volume balance of the noise-making elements and to hear the effect of the modulation from the purple sources is a fantastic way to manipulate sounds on the fly.

The Opsix’s most ear-catching possibilities lay in the sounds of its sequencer and keyboard

A tap-tempo button in the top-left corner allows you to easily bang out the speed at which you’d like the arpeggiator to work its magic and, by pressing shift and mode, you’ll launch the dedicated arp page. Here, you can choose its playback mode, its resolution and its octave range, as well as dial in a gate amount to have things morph from smooth and undulating to spiky and aggressive. The sequencer is even more powerful, letting you record notes and chords on a step-by-step basis or dive into extended functionalities that include the ability to assign not just notes but parameter offset choices to each individual step. This means you can have a different filter offset step per note but might just as easily mean that sequences that begin bone-dry at step one are able to disappear into clouds of smog-thick reverb by step nine and recovered again by their end. It’s magical stuff.

The rule of six

Korg’s Opsix is a deep and rich instrument capable of mind-bendingly unexpected sounds. A quick stroll through its preset list will take you on a whistle-stop cross-decade tour of the kinds of sounds that FM has always done so well: bells and anything with clanging overtones; super-playable and detailed electric keyboard sounds; clavs; Rhodes emulations; warm strings, fruity brass and rich pads. All of which is fine, impressive and diverting. In our tests, we find that the Opsix’s most ear-catching possibilities lay in the warping, bleeping, mangled sounds that benefit the deeper capabilities of the sequencer and the velocity-sensitive keyboard. Remember too that the velocity can be routed freely, meaning that more aggressively played notes can yield sonic variations that go way beyond mere volume control.

To get a sense of what’s possible, you can use the randomise feature triggered via a button in the top-right corner. Use this to change every parameter of the synth or to customise and focus on one module only, such as the operators. It’s a shortcut to the dizzying sonics the Opsix is capable of but still but a taste of what it can do.

ASM’s Hydrasynth is the only other hardware synth we’ve tested in the past 12 months that’s felt so immediately tempting to us. With the Opsix having muscled in on that territory too, we love it for its sequences and the unpredictability offered by the kinds of sounds you’ll hear in Slate + Ash’s Cycles plug-in. Regardless of the musical styles you’re drawn to, if you’re looking for a synth that’s ready to put an individual stamp on the music you make, this is it.

Do I really need this?

Korg Opsix

In addition to the alternatives on p113, Native Instruments’ FM8 is another highly capable FM-based synth. With that in mind, do you even need hardware to acquire FM-style tones at all? If you think not, then that plug-in will please you for a fraction of the cost of the Korg Opsix. But the appeal of the Opsix goes far beyond its physical form. This synthesiser makes FM synthesis playable in a way we’ve never seen before, with sliders you can push and dials you can turn. It also brings new variations to the FM framework, each of which brings sonics all of their own. The question, then, becomes, do I really need an FM synth?
If the answer to that is yes, and you’re drawn to making sounds in a way as yet broadly snubbed by many, many music makers, then the Opsix is an instrument to which you should give proper consideration.

Key Features

  • Altered FM synthesiser
  • Six operators, three EGs, three effects
  • Single filter with 11 types
  • Three LFOs, 23 waveforms
  • Step sequencer
  • Arpeggiator
  • 40 presets
  • Five-mode operator


Ashun Sound Machines
Hydrasynth Desktop Module £800

This multi-talented synth offers FM among many approaches to synthesis. Its semi-modular structure allows the Hydrasynth to act as a front end to modular systems. Pay the extra £500 for the keyboard version.

DX Reface £310

You might think Yamaha best placed to reboot the DX brand and, in a way, they have with this. It’s more than half the price of the Opsix but is far less versatile, offering a fraction of the Korg’s capabilities.


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