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Korg Opsix – A Hands-On Review


I was lucky enough to get hands-on with Korg’s Extended FM synthesizer, the Opsix. What is it capable of, and how could it serve your studio?

Let’s take a closer look.

Meet the Korg Opsix

The Korg Opsix is a digital FM synthesizer that I’ve been able to test out in a hands-on setting. This extremely capable synth has been pretty underrated, so I’ll be making a case for it here.

FM synthesis has a reputation for being intimidating and confusing. However, the Opsix turned out to be a deep but user-friendly machine that’s capable of creating a wide range of sounds.

What vintage synths does it compare to?

The Yamaha DX7 is an extremely popular vintage FM synthesizer. Although not the first of its kind, this synth became the one to bring its sound to musicians all over the world.

It dominated the market throughout the ’80s, quickly becoming an icon of early digital synthesizers.

However, the DX7 was notoriously difficult to program, which meant most users relied on its instantly-recognisable factory presets.

The Opsix has a similar architecture to the DX7 on the surface, which may seem to invite comparison, but Korg have done plenty to set it apart from the classics.

In fact, I think the Opsix has an even more expanded take on FM. The DX7 had a difficult interface, which was part of what made its excellent presets the defining sound of the ’80s.

Achieving a layout and structure that communicates the complicated principles of FM synthesis to the user without overwhelming them clearly proved difficult at the time. However, the Opsix has managed to achieve this and is much easier to navigate as a result – something we’ll discuss more later.

What modern synths does it compare to?

Korg refer to the Opsix as an “Altered FM Synthesizer” and I believe that this is an accurate way of describing it. It’s not just basic FM synthesis that the Opsix is capable of, but a range of similar variations on that foundation.

FM synthesizers have made a comeback in the market in recent years, including the Elektron Digitone and Yamaha’s own reface DX.

However – while these offerings are fantastic, they don’t cover a lot of the same ground as the Opsix.

Aside from the advanced wave morphing and FM capabilities of the ASM Hydrasynth, I can’t think of another product that’s even close to being in the Opsix’s lane in the ability to take and blend FM, subtractive synthesis, and a whole range of alternative modes in a single engine.

Given the prices of these two synths, I think it’s safe to say that the Opsix is a pretty great deal.

How does FM synthesis work?

Lifestyle image of the ASM HydrasynthThe Opsix is a six-operator FM synthesizer. While there are some differences, operators are essentially the FM synthesizer’s version of an oscillator. All six of these operators can be configured in different ways, to function as either a “carrier” or “modulator”.

Carriers are the audible part of an FM synthesizer. Modulators are inaudible but affect the carrier through their modulation, which can be adjusted by controlling the ratio and depth.

The Opsix also features a variety of FM algorithms. While these might seem complicated, they simply dictate which operators are carriers and which are modulators. Algorithms also change the order that these operators interact in, and can set up feedback paths between operators.

Ratio controls adjust the speed of the operator, which can dictate the pitch of the carriers, like an octave control on standard oscillators or speed controls for modulators. There’s a lot more to learn about FM synthesis, but these basic building blocks should help you to understand the Opsix and its architecture. Not as scary as it might seem at first!

The housing

The knobs, sliders, dials, and encoders of the Opsix all feel sturdy and responsive, and the plastic housing is solid and reliable enough to hold up in studios.

The 37-key keybed has a very light action which may bother discerning piano players, but having full-size keys does provide a nice degree of playability.

What’s more, the keys are also very responsive to velocity and aftertouch. I found that a lot of sounds could be radically changed by how hard I played a note or how long I held it. That level of expression is great to have as it creates movement in your sounds and playing.

For live playing, a plastic enclosure and light, three-octave keybed might not be what you’re looking for. Having said this, with a sturdy enough synth stand, the Opsix’s lightweight, portable build might be beneficial,.

For studio-based projects and synth players, the Opsix is very much in-step with the competition at this price point.

The sound of the Opsix

Let’s talk about the overall sound character of the Opsix – this might dictate if the synth is for you.

FM synthesis was ubiquitous through the ’80s, making its unapologetically digital sound a staple of synthpop and mainstream pop of the time.

It’s well-known for evolving, glassy pads, gentle electric piano sounds, metallic textures, spiky bass sounds, and clean bells, all of which makes it excellent for a wide range of genres.

What’s it best for?

Synthwave, ambient, industrial, electro-pop, techno, and cinematic music all spring to mind for me with the Opsix’s sound palette.

While FM typically gives me a sense of ’80s throwback, and the Opsix is certainly capable of those vintage DX7 sounds, a lot of the patches and directions I gravitated towards were more futuristic, industrial, and experimental. I can’t tell if that’s just where I felt like taking the synth, or if that’s where it led me. Perhaps both.

It particularly reminded me of bands like Gunship, Perturbator, and HEALTH, to name a few. So if that’s your kind of palette, this one’s a no-brainer. Some of its subtle, evolving patches reminded me of Brian Eno.

It also made me think of a huge number of video game soundtracks. If you want to get into video game scoring and you’re searching for inspiration outside of the computer, the Opsix might just be one of the most affordable and capable pieces of hardware.

While the learning curve is a lot more gentle than it might seem at first, it’s definitely better suited to the sound designers, as there’s a lot of depth to explore to get the most out of it.

The user interface

When starting to play the Opsix, the main area to start tweaking patches is to the left of the synth’s screen.

The Operator Mixer was a great guide when first getting to grips with the Opsix.

The encoders control the ratio of the chosen operator, while the sliders control the output level, providing a quick and easy way to change things up as you go.

The Operator Mixer

While I was surfing presets to get a feel for the synth, I found the operator mixer a quick and easy way of adjusting sounds while still staying true to the core design of the patch.

It also functioned as a quick and easy way of identifying which operators were doing what, which helped me get a sense of how these sounds were built.

I found I could use this to tweak the carrier levels until I found elements of sounds, and adjust it to taste.

It was also great for removing or softening some of the harsher metallic overtones in certain sounds that I didn’t always find pleasing.

It was a great way of taming some sounds, removing elements, evolving patches, or increasing the intensity of some modulation.

The sound engine


I found the Opsix’s presets offered a great deal of variety, and many were well-suited to the timbres and genres I described earlier.

The operator mixer made it easy to tweak them to fit my palette, even if there were elements I wanted to adjust at first, every sound was extremely usable and I could see many of them easily fitting into tracks.

The Opsix usually has either a squeaky-clean or harsh and metallic sound, depending on how it’s programmed. But as somebody who enjoys pushing the extremes of sound, I personally enjoyed this aspect a lot.

The Opsix is definitely more of a sound designer’s synth. However, it can also do a lot of bread-and-butter synth sounds should you feel the need. The classic FM electric piano sounds are especially alluring, and one of them instantly made me want to play Bon Iver’s “Beth/Rest” on the keyboard.

Operator modes

One of the operator algorithms sets all six operators as carriers, essentially turning the Opsix into a standard subtractive synth with six oscillators instead of the usual two or three.

This is a great option to have, but its focus is and should be its FM capabilities.

If you want more classic sounds, I’d recommend a virtual analog or analog poly synth over the Opsix, however it’s still possible to push it into this territory if you want a do-it-all machine.

The Opsix offers five different operator modes that allow you to really see what the Opsix is capable of.

The main one is, of course, FM. This sound is a lot like taking an audio-rate LFO or second oscillator on a synth and routing it to modulate the frequency of the audible oscillator, although with a great deal more flexibility.

The second mode is Ring Modulation, which varies the volume of carriers instead of their frequency. This gives a familiar metallic sound that was extremely popular on early vintage synths throughout the ’70s.

The third mode, filter, allows a modulator to act as an additional filter, which adds a lot of versatility.

Filter FM, the fourth mode, applies audio-rate modulation to the filter cutoff, a very good way of achieving gritty, noisy sounds, perfect for EDM-style growls.

The fifth mode is wave folding, which will fold the carrier wave on itself, adding subtle texture and emphasis to some frequencies. It tends to work best on simpler waveforms, like sine and triangle waves, although it can still work on other waveforms.

All of these modes offer a huge amount to explore, but it would take a lot more time with the synth and a much longer review to dig any deeper with these features.

The operators

While many FM synths use only sine waves as a basis for their sounds, the Opsix comes with a huge range of different oscillator shapes to apply to the carriers and modulators which helps expand its palette.

It also features slightly lo-fi and characterful 12-bit operators just like the DX7, which are offered in sine, saw, square, and triangle shapes as well as 8-bit operators for even more crunchy character.

These are perfect for vintage ’80s-style sounds. Full-resolution operators can seem a little clean at times and are better suited to more modern sounds.

Korg have also added unique additive waves that’ll be familiar to anybody who’s used the digital engine of the Minilogue XD, and two types of noise.

The additive waves are great at providing subtle, extra harmonics to evolving pads, or a little extra low-end punch to bass sounds.

The noise options are also a fantastic texture to blend into cleaner sounds for a subtler grit or sense of movement.


Of course, no synthesizer would be complete without some good modulation. So the Opsix offers a deep menu from which to shape the movement of your sounds.

Each operator has an individual amplitude envelope to start with, great for controlling the motion and volume of various elements in your sound. This allows you to create unique and continually evolving patches.

The main modulation matrix offers some quick pre-defined routings to help you get started, with envelope generators for pitch, filter, and a third modulation-based envelope.

There are also three LFOs, one for the operator, one for the filter, and one that can be freely assigned. This gives you everything you need to sketch out a quick patch, but it’s quite a limited setup. However, the power of the Opsix becomes clear when you realise this is just the start.

The Virtual Patchbay offers extra flexibility, providing a second menu to create modulations, whilst 12 slots allow you to route almost any source to any destination, with intensity controls to adjust depth.

Everything, from velocity and aftertouch to LFOs, envelopes, and other operators, can be fed into almost any parameter in parallel to where it was already headed. This is where you get real control over your sound.

Last, but certainly not least, the beloved motion recording in the Opsix’s sequencer, as seen on the Wavestate, Modwave, and Minilogue XD, gives you the ability to capture adjustments to parameters by adjusting encoders as you record a sequence.

These motions will then stay in your preset, allowing you to use them while playing freely!

The filters

The next important part of the Opsix’s sound are its filters.

Its default filters are perfectly sufficient and clean, and their flexibility and neutrality lets them fit pretty much any sound. Low-pass, high-pass, bandpass, and band reject are all great options for a wide range of sounds

However, Korg seem to have recognised the clean nature of the standard filters and included analog-modelled filters based on two legendary synths from the company’s past, the MS-20 and the Polysix.

The MS-20’s screaming resonances are extremely unique and distinctive and play extremely well with some of the harsher tones, with both low-pass and high-pass models available.

With the Effect mode on a modulator to load a second MS-20 filter model, you can really take advantage of these emulations to get the metallic dual-filter howl that defines the MS-20. It’s great for basses and screeching leads.

The Polysix model is smooth and gentle, providing characteristic depth in the low end and soft, ambient sounds. It also really shone on more of the traditional virtual analog-style sounds, helping to make them more convincing.

The effects

The Opsix also features a fantastic effects section that can totally transform or add depth to your sounds.

Three slots give you things like modulation effects; a variety of lush reverbs, from plate to huge halls or pitched shimmer; and delays that vary from mono to ping-pong to tape echo.

Korg’s effects are probably some of the best built-in effects available on synthesizers, capable of going head-to-head with some of the most expensive synths on the market.

Usually, synth players favour more expensive outboard pedals to process their synths as built-in effects might not cut it, but I suspect that won’t be the case here. The only option I’ve heard that can rival this effects section are probably those of Arturia, namely the Polybrute and MiniFreak.

Final thoughts

Overall, the Opsix is a unique offering for modern synthesis. It’s a well-designed, great-sounding option that’s suited to anyone looking to explore the boundaries of synthesis.

Whether you’re a producer inspired by more experimental or ambient styles of music; a composer for films, TV, and video games; or a sound designer looking to expand your toolkit, the Opsix will fit right into your studio.

If you’re looking for a more traditional synthesis experience, that’s not really the experience the Opsix is going for.

It offers something new and different, while still paying homage to the vintage synths that came before it.

The Opsix is powerful and deep enough to easily fit any musician looking to break the mold. If you want to set yourself apart sonically and explore new territories, this synth might just be the perfect choice for you.


Content Writer - Live Sound

Callum is a recently graduated audio and music technology student who has a love of punk, rock, metal, and electronic music. He's also a freelance engineer in his spare time, helping local bands make their noise even noisier whenever possible.



  1. Tsutomu Kato

    Can you please tell me what the fourth operator mode is please? You seem to have missed it.

    • Callum Barnham

      Hi Tsutomu,

      The fourth operator mode is filter FM. I described it as a good way of achieving audio-rate modulation of the filter for gritty and aggressive sounds.



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