You may have heard it said that you can never have enough VCAs, but Blaknblu would suggest you can never have enough filters. The Foxtrot quad‑multi‑mode filter has 12 of them. At 38HP, it’s very wide, but the front panel accommodates four individual and complete multi‑mode filter modules, each with a choice of three topologies. The idea is that you’ve got four independent and identical filter channels. Each filter can morph from band‑ to low‑ to high‑pass. You have two mono inputs, dual or stereo outputs, two CV inputs for the cutoff and an assignable ‘Aux CV’ that can control the filter mode morphing, resonance or panning. Lastly, there is a Boost switch for a little bit of overdrive. Behind the scenes is some clever routing to link the filters into a parallel bank controlled by a single cutoff, if you so wish.
Each filter can be one of three types. First, we have the friendly bounce of the Moog‑style ladder filter, followed by the unruly nature of a Sallen‑Key (SK) filter from the likes of the Korg MS20 and, finally, a buttery state‑variable (SV) filter similar to the Oberheim SEM filter. The Boost switch is tailored to the specific filter design to replicate the behaviour of the original circuits when pushed to distortion. Throughout the Foxtrot, the topology is digitally modelled virtual analogue, as opposed to actual analogue circuits, but there’s nothing in what you hear that would suggest these are anything other than classic analogue filters.
The modes themselves are helpful in broadening the appeal, but being able to sweep between them with an LFO or source of rhythmic voltage gives it a whole other personality.
One thing you don’t see very often is CV control over the filter mode. The modes themselves are helpful in broadening the appeal, but being able to sweep between them with an LFO or source of rhythmic voltage gives it a whole other personality.
All of this is great in a single‑filter module, but this has four. Using them independently is naturally useful in any rack. If you were looking into polyphonic modular, then a slab of four identical filters would be perfect for a four‑voice system. In fact, Blaknblu also make a similarly featured quad VCA called Alpha Pro that would complement that endeavour beautifully. However, it’s the linked operation that gives the Foxtrot its superpower.
Flick two or more of the filter channels to On, and they will become linked. The audio outputs are summed to every output, and the filter cutoff is added to the leftmost filter meaning that you can sweep all of the linked filters from the left filter. With a single input, you find that you can add filter after filter to your signal chain. You can tune in four band‑pass filters and then shift them together, or you can link a cascade of different filters, all modulated in different ways, creating complex spectral shifting. Even running two filters side by side with an oscillator in each gives a dramatically different tone when linked and unlinked.
It all hangs together heroically in the face of so much filtering, especially when pushed against the limits. If I had to find a fault it would be that the patch socket layout is a little unintuitive, and I keep grabbing the mode knob, thinking it’s the cutoff because it stands out more. I’m also not convinced I’d be making full use of its features very often and in my overloaded rack every module needs to earn its space. However, it does sound pretty fantastic.
If you’re drawn by the idea of these three filter models but can’t quite cope with the enormity of what the Foxtrot has to offer, you’ll be pleased to hear that Blaknblu have just released a single‑channel stereo version called the Foxtrot Duo. This feels like a solid move, as for all the Foxtrot’s versatility I can’t help wondering whether the scale and scope is a bit much for most people’s racks.
£420$573.99