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Expressive E Osmose

Polyphonic Synthesizer By Robin Bigwood
Published April 2023

Expressive E Osmose

Expressive E’s Osmose is a synthesizer like no other.

The quest to make keyboard‑based synths expressive has taken quite a journey over the decades. First there were levers, wheels, pedals, the odd touch strip and breath‑controller input, and keyboard aftertouch. More recently we’ve seen more radical experiments in form factor, underpinned by the MPE (MIDI Polyphonic Expression) protocol: they include ROLI’s Seaboards, KMI’s K‑Board and Roger Linn’s Linnstrument.

Now there’s another option, in the form of Expressive E’s Osmose. This was announced by the French company back in 2019, with a launch planned for later in 2020. But with the small intervention of a global pandemic, it’s taken until now for production to go into full swing and units to start getting out to purchasers.

Two things mark out the Osmose as substantially different to its obvious MPE‑friendly competitors. First, it has what might appear at first sight to be a conventional keyboard action, with full‑size black and white keys. A totally different kettle of F#s from the Seaboard’s squishy continuous silicone rubber surface, the K‑Board’s hard strips, and the Linnstrument’s fret‑like squares. Actually it’s far from conventional, as we’ll see in a minute, but it’s relatively more so than any other MPE keyboard to date.

Second, it has a built‑in synth engine. So for the first time since the original (but now long‑discontinued) Seaboard Grand we have a complete, stand‑alone, relatively affordable expressive synth that doesn’t rely on compatibility with soft synths running on an attached PC. That gives the potential for tighter integration between touch and sound, and better immediacy and ease of use. Control of software and hardware synths is still entirely possible, though, via USB or DIN MIDI (and even CV: see the ‘Additional Expressive Control’ box for more about that).

So it’s all a fascinating prospect, and it’s here at last. So, after such an extended billing, does the Osmose reality live up to the hype?

The Osmose measures 894 x 316 x 87.5mm and weighs in at a considerable 8.3kg.The Osmose measures 894 x 316 x 87.5mm and weighs in at a considerable 8.3kg.


The Osmose is quite a hefty unit, weighing in at 8.3kg, and measuring 894 x 316 x 87.5mm. The base and sides of the casework are a tough plastic, and the top panel is metal. The construction quality feels really good: it’s a classy product.

Up top, various controls surround a high‑resolution colour LED screen that offers good visibility and contrast from almost all angles. The buttons include dedicated preset up/down recall and octave transposition up to two octaves in either direction. There’s also a pair of fader‑like handles, one sprung and one not, in the normal way, for pitch‑bend and modulation. None of the buttons and encoders surrounding the screen have a dedicated function but are ‘soft’, relating to what’s visible on the screen next to them. The endless encoders can also be push‑clicked to confirm settings and so on.

Rear‑panel connections include a stereo pair of quarter‑inch pseudo‑balanced TRS line outputs, two quarter‑inch pedal inputs, a USB‑B socket, DIN MIDI In and Out, and an inlet for the supplied 12V 1.5A centre‑positive external PSU. The power plug can be locked in place with a quarter‑turn, which is a nice touch. On the front there’s a stereo quarter‑inch headphone output with a sprung, retractable volume knob.

The Osmose’s rear‑panel connections are gathered together at one end and include MIDI I/O sockets, a USB‑B port and quarter‑inch audio outputs.The Osmose’s rear‑panel connections are gathered together at one end and include MIDI I/O sockets, a USB‑B port and quarter‑inch audio outputs.

The main event, however, is the keyboard action itself, which sits proud of the casework in an unusual way. The full piano‑sized keys (with white keys a notably long 152mm) have a matte finish, and in most ways look entirely normal. Much less so though are the black extensions of the key levers, going back a further 85mm towards pivot points at the rear. And from there on it gets more unconventional still.

Keys have an initial dip of about 9mm to a first point of resistance. Keep pushing though and they’ll go much further: for white keys, at least as far again, and for black another 4‑5 mm. Massively more than the (at most) few millimetres of aftertouch movement offered by a conventional synth action, and far smoother and more fluid in feel.

And here’s the bombshell: the keys also move from side to side. Black keys subtly rock up to about 4mm both left and right at all times. White keys can’t move much at rest, but as soon as you depress them even a millimetre or so they’ll wiggle almost as far, staying horizontal as they do so.

As you might expect, these novel dimensions of key travel are intimately involved with the expressive response of the Osmose. The left and right X‑axis movement is essentially for key‑driven pitch bend, so you can wobble your fingers for vibrato. Pitch‑bend amount is determined by the patch, but even then, there’s the scope for different players’ vibratos to be quite unique. Single finger touches easily activate it, but you can go further by supporting a key‑front with your thumb, for example.

The initial and aftertouch‑like key dips have some similarity in playing feel with what conventional synths offer from their velocity and aftertouch phases, but in reality the situation is more complex and subtle, and capable of vastly greater expression. To understand it, for the purposes of this review, we can do it the easy way or the hard way... Actually let’s do both.

Osmose Easy

Using various onboard synth sounds, it’ll take most players only seconds to realise the Osmose key response is not like other synths, even those with polyphonic aftertouch. Many sounds begin to speak from just the lightest touch, of only 1 or 2 mm. Further exploration of the key dip is generally met with greater volume or intensity, or some kind of timbral variation, and with an impressive speed and finesse of response. Perhaps it goes without saying that this is delivered with typical MPE‑like independence from key to key: so one key can be swelling, as another is vibratoed, and another is released.

At the same time, many sounds that can be ‘squeezed’ into, smooth as treacle, will produce attacks that positively jump out of the speakers if you tap or fully depress the key more quickly. Some sounds will trigger another range of responses when you let go of the keys at different rates. Yet others offer staggered attack points, with discrete events at perhaps 2, 4 and 6 mm into the key dip. Or, all of these things combined.

I was expecting the Osmose key action to be expressive, in some general sense. The reality is more sophisticated and musically potent: it’s a truly exquisite level of sensitivity on offer, with a feeling of in‑the‑moment immediacy that can be breathtaking. Yes, it’s a simple synth‑like keyboard, in one sense. But this action also has aspects of response that are closer to various percussive instruments, perhaps hand drums or metal pans. Or, just as often, it gives the sensation that your finger has become bow‑ or breath‑like. The very high level and speed of integration with the sound engine is no doubt crucial in supporting this. There’s also a real feeling of ‘aliveness’ in many sounds, with a degree of timbral complexity and development that is beyond most virtual analogue synths.

I was expecting the Osmose key action to be expressive, in some general sense. The reality is more sophisticated and musically potent: it’s a truly exquisite level of sensitivity on offer, with a feeling of in‑the‑moment immediacy that can be breathtaking.

Osmose Advanced

So that’s how it feels. How does it work? Well, the integration with the onboard synth engine really is important. The synth is called the EaganMatrix, and is identical to that used in one of the most long‑established and sophisticated (but also expensive and rare) expressive instruments, the Haken Continuum. Indeed, the Osmose is a formal collaboration between Expressive E and Haken Audio. More on those names by the way: Lippold Haken is the inventor of the Continuum, and also a DSP algorithm developer and professor of Electrical and Computer Science at the University of Illinois, while Edmund Eagan is the developer of the Continuum/Osmose software editor and principal sound designer for the system.

The Osmose’s internal control scheme is not based on MPE MIDI but an extension of it termed MPE+ that improves resolution in the domains of time (for very quick response) and magnitude (for very smooth). Interestingly, it does away with the concept of key velocity (or, in MPE terms, Strike Value) completely, and instead derives note onset information from ‘attack trajectory’, a much more precise assessment of key travel over time that can take into account key dip as well as rate and acceleration.

Another notable point: Osmose offers no response at all to front‑back (Y‑axis) finger position, which is a key element of continuous playing surfaces like the Continuum and more recent Seaboards. Instead it generates this Y‑axis data from the ‘aftertouch’ part of the key stroke.

MPE+ generates some dense data streams, but they are only ever exposed (and of concern) if you want to record a stand‑alone Osmose performance to a MIDI sequencer. That’s done using a dedicated second virtual USB MIDI port.

However, the Osmose will function perfectly well as an MPE or basic MIDI controller. It does that by deriving velocity data (or MPE Strike Value) from the initial key touch, and various types of channel or polyphonic pressure from the aftertouch. An ‘Ext MIDI’ mode, with a dedicated button, toggles the Osmose’s interface entirely over to MIDI control functions. And then a handful of dedicated MIDI control profiles are provided, including a full MPE implementation, ‘classic keyboard’ (which turns off all expressive features except velocity and channel aftertouch), and ‘poly aftertouch’ (which gives good compatibility with synths like the Oberheim OB‑6 that offer this response, but not full MPE). The point in the key dip at which notes trigger varies between modes: higher/earlier for MPE, and lower/later for ‘classic keyboard’. That’s some real sophistication, and very nicely considered.

Inside The Matrix

Let’s turn now to Osmose’s internal synth, the EaganMatrix. It’s lifted straight from the one used in recent versions of the Haken Continuum, running on six custom SHARC DSP chips, and supporting up to 24 notes of polyphony, often realised as 12 stereo voices. It’ll do multi‑oscillator virtual analogue, FM, physical modelling and a kind of granular synthesis, amongst other things, but there’s no sample replay aspect. It’s essentially monotimbral: a bi‑timbral keyboard split is apparently technically possible, though not currently supported on the Osmose. Having said that, the impression of multitimbral layers, with perhaps a percussive element alongside a sustaining pad, say, is entirely feasible given the flexibility of the synth architecture. Which is extensive...

There are five flexible oscillators/waveshapers plus additional noise sources, five multi‑mode filters with various slopes, two filter banks with eight or 48 related filters (which also act as the basis for various types of physical modelling, granular and additive synthesis), time delays (which support chorus and flanging as well as another kind of physical modelling), shape generators, a convolution module, and a ‘recirculator’ for various types of delays and reverbs.

An EaganMatrix formula takes real‑time inputs from the keys and modifies them in various ways, to control audio or modulation signal flow in the matrix. It’s not for the faint‑hearted, but gives tremendous control over touch response.An EaganMatrix formula takes real‑time inputs from the keys and modifies them in various ways, to control audio or modulation signal flow in the matrix. It’s not for the faint‑hearted, but gives tremendous control over touch response.

The way it sounds can, to my frequently synth‑pummelled ears, be very fine indeed. It’s a good sign when factory presets sound good despite not dripping with reverb and other effects, and the Osmose’s aren’t. What then comes out of the EaganMatrix is a vast gamut of timbres: purely synthetic tones that sound like Moogs or Oberheims one minute, and complex, turbulent physically modelled wind, string and guitar or bass sounds the next. Some patches defy description completely, and can even be several sounds rolled into one: perhaps a multi‑layered slow pad and a sharp pluck, either ready to be teased out with the key action in Jekyll and Hyde fashion. Things can be really very warm, lush and ‘analogue’; twangy and edgy like a modern FM synth; or dark, noisy and complex like the best plug‑in physical modellers and granular synthesizers. A real timbral chameleon.

All the factory presets, over 500 of them, offer six sound control macros that often dial in timbral variations, changes in response speed or effects depth from the Osmose encoders. Similarly accessible global effects include reverb and five types of delay, EQ, and a compressor/gain module. Tweaked presets can be saved to one of 128 user memory slots.

As well as this tremendous timbral range, there’s often a unique sort of complexity too. I mentioned the sense of ‘aliveness’ before, and there’s a further liquid or organic quality in many sounds, even those that are in every other way completely electronic in style. I found it really beguiling.

It’s no exaggeration to say that during testing I got lost in many individual factory presets for an hour or more at a time, with the Osmose seeming to open doors and spark creativity in a way that I’ve only rarely experienced. Or that maybe is more often associated with acoustic instruments. It’s a really special, wonderful synth. Though what it’s not, I hasten to add, is anything much like a sampler: there are sounds that are a bit like a sax, or flute, or cello, and you can solo using them with amazing expressivity, but they’re unashamed synthetic equivalents.

The flip‑side of the EaganMatrix is its programming interface, which for many of us will require a paradigm shift in the way we think about synths. To put it in another way (and horribly mangle both a metaphor and a great quote), in this matrix Kansas has definitely gone bye‑bye.

In the Haken Editor software there are no familiar knobs or sliders, or even readily identifiable ‘modules’ like oscillators, filters, LFOs or envelope generators. But it is a massively modular design, in which you patch sources to destinations at intersections on a grid. Think VCS3 pin‑board, but rather than pins you place numbers (mathematical constants, for fixed signal flow), inputs from the Osmose playing surface (with letters W, X, Y and Z corresponding to gate, pitch, aftertouch and initial touch), and ‘formulas’ denoted with a letter‑name. These are the hardest bit to understand at first, but are essentially mini‑algorithms that can take in all key‑touch inputs at once, and do anything with them from simple scaling and limiting to more complex algebraic mathematical operations.

The ‘problem’ with the EaganMatrix is how alien it feels at first if your experience of synthesis is primarily knobby hardware or software synths. Also that it is not readily tweakable, and for even apparently trivial adjustments (relative opening or closing of a filter, or changing the rate of an LFO) it’s close to impossible to know where to start. How factory patches are constructed will also be a total mystery until you are much more experienced with the system.

However, it is quite possible to learn, and structured tutorials are provided with the editor download. They’re not exactly a walk in the park, and it doesn’t help that they were written solely with the Continuum rather than Osmose in mind, but in the few days I had looking at them I made useful progress. And I’m a decidedly un‑mathematical creature. Perhaps we should consider that in the same way some people take a course to learn Max, Pure Data or SuperCollider, that’s the price of entry for the EaganMatrix as well. I do wonder, though, if in the future we might see a version of the editor that presents a much friendlier, graphics‑driven interface, hides the full matrix but pulls appropriate strings behind the scenes, and trades some open‑endedness for ease of use. That’s pure speculation on my part, but it seems an eminently sensible direction of travel.

The Osmose software editor runs in Cycling 74’s Max, which it’s not necessary to own: apparently the demo version supports the editor just fine. There is logic and clarity here, but if you’ve come from a knobby hardware synth you may wonder what planet you’ve landed on.The Osmose software editor runs in Cycling 74’s Max, which it’s not necessary to own: apparently the demo version supports the editor just fine. There is logic and clarity here, but if you’ve come from a knobby hardware synth you may wonder what planet you’ve landed on.

Forward Osmosis

It’s a massive achievement for any company to bring a successful, well‑rounded product to the market. To do that for an MPE‑type instrument, which is normally so niche in its appeal, which rewrites the rule book again, and can’t draw on much if any existing tech, is extra‑special. With that in mind, I think what Expressive E have achieved with the Osmose is truly staggering. Personally, I think it’s one of the most exciting electronic instruments to appear in a long time — I’m even tempted to say ‘ever’ — and there are a few reasons for that.

First, that remarkable keyboard action, which simultaneously feels so familiar, works so intuitively, and yet can support such a wide range of novel gestures and playing techniques. And which could open up whole new worlds of expression and sound interaction for keyboard players and composers. I was concerned at first that the lack of front/rear position sensing represented a step backwards compared to other MPE products out there, but in real terms, very little flexibility is lost. Thinking about ways continuous surface controllers are played, Y‑axis movements are often made subsequent to the initial touch, so in that sense implementing them in an aftertouch‑like phase in the Osmose makes little difference in the real world, and is probably easier to control to boot.

Second, the built‑in sound engine. Yes, it’s currently a good challenge to program, but more importantly the integration with the keyboard action is pretty much flawless, sometimes apparently magical, and it is both super‑flexible and extremely nice sounding. The quality and consistency of the factory presets is high, and the combination of touch‑ and macro‑driven sound variation should mean that you will neither immediately sound like the next guy/gal, nor constantly be wishing you had a full synth‑like control panel in front of you. Being able to play the Osmose without a computer in sight, if necessary, feels right in keeping with a broader aesthetic of simple, direct, immediately realised expressivity.

MIDI control functionality is also valuable, and really successfully implemented. Some other MPE controllers are, quite honestly, pretty lousy in this regard, away from a small subset of dedicated or compatible software. Even with the Osmose, you may still need to do some extensive re‑working of patches on third‑party synths that purport to be MPE‑compatible before you have anything musically useful. However, the ‘normal’ moving keys, dedicated MIDI control mode and simple profiles make the Osmose absolutely viable for general, day‑to‑day work with your DAW or hardware modules. It’s only a four‑octave keyboard, of course, and the springy, somewhat malleable action isn’t what I’d choose first for piano sounds, but I wouldn’t hesitate to use it for most synth or sample‑library duties.

As for anything that could use improvement, there doesn’t seem to be much. We could wish for a knobby EaganMatrix spin‑off, I suppose. And whilst the onboard operating system is on the whole very slick and friendly, just occasionally the screen/button/encoder interactions are a bit non‑intuitive, with some lack of consistency about how you navigate, select and ‘validate’ settings and lists. Expressive E told me that there are plans to allow custom MIDI control templates to be saved in a future firmware, and that would be a really useful development. On the review unit I saw one trivial hardware glitch, with the centre position of the pitch‑bend fader sometimes generating a dribble of data, but this seems to be more a matter of calibration, and the size of the ‘null’, and can also be fixed in firmware.

The Osmose is a synth that’s truly unique, surprisingly versatile, can be hugely inspiring, and sounds very, very good indeed.

In the end, what we have in the Osmose is a synth that’s truly unique, surprisingly versatile, can be hugely inspiring, and sounds very, very good indeed. The fact that it’s relatively affordable, with a price lower than that of many other conventional polysynths, analogue or not, is the icing on the cake. In a synth world that sometimes seems fixated with churning out the same old, the Osmose stands as a paragon of strange, wonderful otherness. With a doubtless growing user base and further development in future it’s going to be interesting to see how deep this rabbit hole goes.  

Pressure Glide: Additional Expressive Control

One important aspect of the Osmose’s touch is called ‘Pressure Glide’. To some extent this works around the fact that the Osmose’s playing surface is not continuous, so can’t support the same kind of intuitive Theremin‑like swoops as a Seaboard or Continuum. What it does is to allow any pitch intervals up to a user‑defined maximum to trigger a legato/portamento transition, like on a monosynth. So if your max was two semitones, then you can still play polyphonically, but any notes two semitones apart or less will become intertwined to produce a single note, the pitch of which changes as you rock the pair of keys in a see‑saw fashion. Much easier to understand in practice than to describe! It’s a pretty nice compromise between the discrete key and continuous surface approach. Pressure Glide opens up various new playing gestures, like up/down flicks of the hand, as well as really slow glissandos, and you can turn it on and off easily while playing.

There’s a further playing technique available, which is far from obvious. On the black lever extensions behind the main part of the Osmose keys you can easily do semitone glissandos, and if your touch is sufficiently tenuto and Pressure Glide is on, then quasi‑continuous glides over big pitch ranges are possible even when the glide interval is small.

Then, not employed much in the factory presets but lurking in a ‘Playing’ tab is an extremely good arpeggiator. It has 10 parameters, many of which can be modulated in real time by control inputs from keys, wheels and pedals. All sorts of things are possible, like expanding the octave range or triggering ratchets with aftertouch — for individual notes in a held chord if you vary your touch appropriately — or controlling gate length with a pedal. Eleven factory presets are provided, and you can save your own creations too.

Some MPE synths do away with pitch‑bend and modulation wheels: the Osmose wears its pair quite prominently, and they’re useful to have for several reasons. The pitch‑bend is good for general MIDI control, when key vibrato is turned off, or for when you want to bend pitch further than finger vibrato allows. The mod wheel is also often tied to one of the internal synth macros, and can conjure important variations in each sound a little more quickly than the encoders.

The same goes for the pedal inputs, which are configurable for expression pedals (a list of the most compatible is on the Expressive E website) and switch or continuous sustain types, with settings and calibration procedures in the Osmose’s global settings.

Finally, there’s an optional add‑on for the Osmose: the Haken CVC (Continuum Voltage Converter). This will be of interest to analogue and modular synth users who want to explore response rates that vastly outstrip MIDI or MIDI‑to‑CV converters. The $549 oblong lump interfaces with the Osmose DIN output when it’s been switched to a proprietary high‑speed mode. You can then plug‑in a couple of your Moog System 55s, or whatever, and enjoy four polyphonic voices with independent control streams for pitch, initial pressure and aftertouch, scaled if necessary via the Haken Editor software.


  • MPE‑like (and better) expressivity delivered through a ‘normal’ moving key action.
  • The onboard synth sounds superb and is beautifully integrated with aspects of touch.
  • Eminently usable as both a simple and MPE‑ready MIDI controller, via USB and DIN.
  • Fine build quality, friendly interface, and apparently excellent software stability to match.


  • Full patch editing on Mac/PC only, via Max, and will require investment of time, and courage.


A paradigm‑busting, deeply expressive synth and MIDI controller that is both audaciously innovative and reassuringly familiar.