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Supercritical Synthesizers Neutron Flux Filter

Eurorack Module By Rory Dow
Published December 2021

The Neutron Flux is a chameleon. Supercritical describe it as an “8‑pole variable character filter”. It has an analogue core with digital control. It’s a stereo filter and can morph smoothly between different ‘characters’ giving you almost endless tweakability to dial in just the right tone.

Supercritical Synthesizers Neutron Flux: 12HP, +12V 150mA, ‑12V 120mA.Supercritical Synthesizers Neutron Flux: 12HP, +12V 150mA, ‑12V 120mA.There’s a lot of filter packed into this 12HP skiff‑friendly module. The 8‑pole filter is, in fact, two 4‑pole filters. They can operate in parallel (4‑pole, stereo) or series (8‑pole, mono). The Poles button will cycle around options from 1 to 8 poles. With some filter characters, these options don’t select poles exactly, but they will usually change the response going from shallow to deep.

The filter characters are arranged in three banks of five for a total of 15 (at least so far, Supercritical added five of those with a firmware update mid‑review). They are accessed with a knob in the centre of the front panel which is flanked by five LEDs labelled Fat, Crisp, Liquid, Sour and Mean. These labels won’t always describe the current filter character because that depends on which bank you’re in.

The first bank contains a range of classic filter types with descriptions that allude strongly to their origins (and do match sonically with the labels on the front panel). There is an east‑coast ladder filter, a creamy state variable, an OTA, a ‘liquid acid’ filter and one described simply as ‘screaming’ (a banshee let loose by accident during development apparently). You can probably work out which famous filters most of them are designed to sound like.

The second bank goes off‑piste. It contains dual resonators, a Chebyshev filter (I had to Google that one!), phasers‑style notch filters, distortion and even waveshaping oscillators. The third bank, new to the v1.3 firmware which should be available by the time you read this, contains formant vowel filters — A, E, I, O, U, OE, Y and AE.

The current bank of filter types can be morphed from one to another using the Character knob or its corresponding CV input. Morphing is very smooth and there is a whole world of filter characteristics and other effects to be found in the ‘in‑between’ states. I can’t express enough how adaptable this filter is in that regard.

In addition to the filter‑type morph control, there is a Mode control that morphs from low‑pass, through notch‑ or band‑bass, to high‑pass. Having filter type and mode on separate controls, both morphable, opens up a world of Olympic‑standard filter gymnastics.

As well as the obvious cutoff and resonance controls, there is input drive, which provides plenty of gain (and gain reduction). The overdrive sounds excellent, with resonances becoming more unstable until the signal collapses into chaos (the good kind). If you need more, there’s even a +20dB boost which can be activated by a secret button press.

Neutron Flux offers many more modes than your average filter and can morph fluidly between them. It can emulate many standard filter types, or provide interesting new filter alternatives. It can be clean and polite or filthy and rude.

The Stereo control shifts the frequency of each of the dual‑filters to create offsets between the left and right channels. At times, I found myself wishing this control went further. The maximum frequency offset can be quite subtle, although it does depend, to some extent, on the filter type and mode. It’s still a nice way to get left and right channels undulating fluidly and when frequency modulating at audio rates, this can produce super‑wide effects from a mono source.

In terms of CV control, the Neutron Flux has plenty to offer. A 1V/oct input for frequency tracking is available alongside a more general FM input, which has a bipolar attenuation control. There are also CV inputs for Mode, Character, Resonance and Stereo control.

The Neutron Flux offers many more modes than your average filter and can morph fluidly between them. It can emulate many standard filter types, or provide interesting new filter alternatives. It can be clean and polite or filthy and rude. I was impressed with just how many different sounds I could get with the same input material. It could make Moog‑like bass lines one minute, 303‑acid the next, then it could morph to something brutal sounding that put me in mind of my trusty Sherman Filterbank, finally moving on to provide cool, clean, stereo FM pad movement. Even on its own, it can be a source of self‑oscillating stereo effects.

The price is quite high, but you do get a very flexible filter for the money. If you’re short on space and looking for a stereo filter that can sound like a dozen other filters, the Supercritical Neutron Flux could be a strong contender.

£409 including VAT.