You are here

Xaoc Devices Sofia

Eurorack Module By William Stokes
Published June 2023

Xaoc Devices Sofia Eurorack Module.

You’ve heard ‘never judge a book by its cover’, but how about ‘never judge the gear by its faceplate’? It’s a principle I must constantly remind myself of in the studio; by this I mean that so many guitar pedals, plug‑ins and, of course, Eurorack modules look and feel so lovely (and occasionally so hilarious) that it’s actually easy to forget the most important thing: the sound. In fact, it’s now got to the point where the worse or more boring something looks, the more inclined I am to see what it can do — and inversely the prettier it is the more sceptical I am.

Needless to say, then, my eyebrows were raised upon unboxing the Sofia from Polish developer Xaoc (pronounced 'Chaos') Devices. Even the module’s full name is suspiciously pretty: the Sofia Transcendent Waveform Analog Oscillator Model Of 1955. Putting the lovely included Xaoc Devices red tote bag and paper manual to one side, I picked up the module and tested its knobs and switches, as I’m in the habit of doing. A perfectly weighted stepped dial for octaves above a large, classic‑looking frequency knob, four sliders, six smaller knobs, all beautifully firm and smooth to the turn. A gorgeously designed silver and black panel with a vintage look that would fit right in at the venerable PRES (Polish Radio Experimental Studio)... It’s all just a little too lovely, right? Wrong. From the moment I mounted it and powered up my system it was clear that this module sounds every bit as good as it looks and feels, and then some.

So, what actually is the Sofia? And what makes it transcendent?

Well, it’s an oscillator. And almost certainly unlike any other oscillator you’ve tried. At the heart of the Sofia is something called fonction d’onde formantique, or FOF. FOF synthesis is essentially the synthesis of vocal‑like formants without filtering, achieved by superimposing decaying sinusoidal tones onto each individual cycle of a fundamental base waveform. In this way it ostensibly mirrors what the Sofia manual describes as the “parallel acoustic resonant filters that produce decaying sinusoidal tones in response to each pulse of air pressure from the larynx”. In other words, the way a human voice behaves to achieve complex waveforms. Viewed on an oscilloscope, these decaying sinusoidal tones (I can’t help but feel that term sounds like some kind of nasal infection) look like waves ‘rippling’ through each cycle of the base wave, which is why they have come to be known, at least for the purposes of the Sofia, as ‘ripple elements’. The Sofia generates two such ripple elements that both work on the same sine base wave. Their characteristics can be adjusted, multiplied and modulated in all manner of ways, and their harmonic contributions can be mixed in any combination — that is, relative to each other and relative to the base wave, which is itself slightly saturated for that extra bit of character.

While this workflow takes some getting used to, it’s a wonderful way to go about sculpting sounds, and at the end of the day it sounds, frankly, excellent. I love Xaoc’s description of the module’s palette in the manual: “a wide range of acoustic, woody, organic and animal‑like, as well as high, fuzzy and bright sounds”. Couldn’t have put it better myself. Even when patched to simply drone away, moving various parameters from one extreme to the other creates three dimensional movement that at times sounds like a toothy pair of sync’ed oscillators, at others like 303‑style resonant filtering, and at others still like some kind of bubbling, frozen vocoder.

It achieves this range with surprising simplicity. Beyond the aforementioned octave dial and frequency knob, the Sofia’s panel offers three controls for each of the two ripple elements, all with accompanying CV inputs. There are two controls in the first instance: one to blend between the fundamental tone and the ripple elements with all their wondrous overtones; and one to control the balance between ripple elements A and B. Beyond this, both ripple elements have identical controls: Ratio, which adds cycles (and therefore harmonics) to the ripple wave; Damp, which controls the decay rate of the ripples’ amplitude through each cycle of the fundamental tone; and Warp, which alters the density of the ripple wave: the ripples can get denser as they move through time, or they can get sparser.

The cherry on top of such harmonic richness is the fact that the Sofia offers a whopping six possible outputs. Unite any combination of these with a mixer and you can achieve astonishing width and movement...

This, of course, is just the theoretical side of things. There’s no way you can track these effects in detail just by listening to them — at least, not in the way you can with a conventional envelope, since everything is repeating at audio rate. It’s therefore well worth keeping an oscilloscope to hand if you have one, at least in the beginning, just to keep tabs on what’s actually going on. It’s also fascinating, to be honest.

The main thing, of course, as we have previously ascertained, is how it sounds. So it hence became a simple case of exploring with my ears how each of these controls has its own way of squeezing, stretching and twisting the sound of Sofia. On top of this, it’s possible to switch between sine and square waves for the ripple elements, square of course being more angular and harmonically rich. Things really come alive with modulation, and self‑patching is encouraged. Even the simplest of LFOs coaxed out tones ranging from visceral to ethereal; add some reverb, and wow!

The cherry on top of such harmonic richness is the fact that the Sofia offers a whopping six possible outputs. Unite any combination of these with a mixer and you can achieve astonishing width and movement, for example keeping the fundamental wave down the middle of the stereo image and panning the ripple elements left and right. Fantastic. An astonishingly powerful and flexible module, the Sofia has absolutely become one of my favourite oscillators and I would recommend it to anybody. Whoever said looks could be deceiving?