Zorx Electronics
SF1 Dual / Stereo Filter - Weston Precision Audio

SF1 Dual / Stereo Filter - Weston Precision Audio

by Ellison Wolf

There’s a lot to be said for what you name a child, pet, or business, and Weston Precision Audio has to be pretty confident about their technical ability to add that “Precision” in there. It’s not just something you throw out there; you’ve got to own it. As it stands, this Portland, Oregon-based company more than lives up to the task. They’ve been offering impressive DIY projects [take a look at their PRO2021 Pro-One monosynth project] as well as completed modules for a bit, but up until now I’ve only been able to admire their modules from afar, never having been in close proximity to one. I'm happy to report that’s now changed.
SF-1 is a really nice-looking thing; right out of the box I like the rounded PCB corners, if for no other reason than they look clean. It might seem arbitrary, but details like this, this design thoughtfulness for a seemingly small detail, might just perhaps contribute to the “Precision” in their name. It’s always a bit fascinating to see what other people notice, what they deem worthy of facilitating awareness, attention, and/or change in, and you can tell how much love is put into SF-1. The overall build quality is great, as the module feels very solid and even the three-way switches—something I don’t normally pay much attention to—are sturdy and rise above the norm, reminding me of the switches found on some vintage drum machines. The black, gray, and yellow color scheme of the module is appealing and different, though not too much—it will still look as good in your dark and stormy all-black setup as it does mine—and the panel, while not flashy or overly design-y, looks good with nice, clear, and legible text and a pleasing mirrored horizontal symmetry.
As with most dual filters SF-1 can act as two separate filters—the Left side and the Right—with multiple simultaneous outputs. The Left side’s input is normalled to the input of the Right so that with one input you can get up to four related simultaneous outputs, and there’s a Link button whereupon you can control the both sides of the filter with just the Left controls.
Each side lets you select between a 2-pole [12dB per octave] or 4-pole setting [28dB per octave], and there are controls for Cutoff and Resonance with CV inputs for both [with the Cutoff CV input going through an attenuverter]. Input level controls for each side let you tame your signal, and can also add some grit, some overdrive to your signal when pushed. 1V/Oct inputs for both Left and Right are available and SF-1 self-oscillates quite easily and tracks well.
One of my favorite features on SF-1 is the inclusion of a dual VCA crossfade/panning circuit [with CV input], which integrates some interesting channel behavior and brings in stereo action to the module. On this control dead center means an even mix of both Left and Right channels at each output, and panning to the extremes isolates each channel into a respective output. When you start modulating this is when it becomes apparent how powerful this can be.
Another excellent feature, perhaps the most obvious one, is that SF-1 are the various simultaneous outputs and available filter types that each channel offers. The available filter shapes for each are: Low Pass, High Pass, and Band Pass for L1 and R1 outputs, and Notch, All-Pass, and Phaser for L2 and R2 outputs. The first three options are pretty standard fare, and do exactly what you expect. The last three options, however, aren’t very common with modular filters, and I’m not sure I’ve ever used a notch filter—which filters out a specific, typically quite narrow, range of frequencies—or an All-Pass in modular before. I’ve used notch filters in studio recording and mixing to get rid of competitive frequencies or to clean up a sound or something, but never in a modular setting or live performance realm in real time. I always like when you’re able to use something that’s typically thought of as a utility, like a notch filter, in unique and interesting ways, and it’s cool that SF-1 lets you explore in this way. Running the output with the notch setting, and through a spectrum analyzer as I did with my beloved DATA, you can just twist and turn until you find something cool, and it’s a pretty fun exercise to correlate the sound with the frequencies lost and/or gained with each knob twist.
As cool as the Notch filter is, I have to give it up to the All-Pass. I didn’t even know what one was until I saw it on this module, and if you just patch out of it without any fanfare, it doesn’t sound like much. Well, that’s because it isn’t. The frequency boundaries are pretty extreme so that it just sounds like it’s letting all frequencies pass through it, hence the name. The fun—and I have to say, it is very fun—begins when you start modulating the Cutoff for each so that you get some phase modulation. Doing so on both sides while unlinked and with the Resonance cranked on both sides and introducing some panning into the mix and you’re really cooking. The movement of the sound was nothing short of spectacular.
Having just received a Schlappi Three Body I decided to patch up a simple melody line into it with some phase modulation dialed up in that module and then patched one sine wave output from a single channel of the Three Body into the Left input of SF-1 using the All-Pass output on both channels—panned hard left and right in my mixer—and with some modulation going into the Cutoff CV ins on both sides for some stereo dual phase modulation. I’m not sure what you’d call patching a phase modulated sound source into a phase modulating filter, but whatever you call it, it was pretty bonkers, and if I’d had a phase-phasing phaser that was really phasable who knows what would, or could, have happened. Maybe I would have entered a new dimension in time or space. Dunno.
Speaking of phase, the Phase setting is pretty fun as well, and can get very wobbly, especially if you unlink the two filters and move the cutoffs around to find your sweet spot.
I had to pry myself away from the L2 and R2 outputs to check out the more typical filter shapes that SF-1 has, the LPF, HPF, and BP. Those all sound nice and do what you’d expect, and at 24dB both the LPF and HPF can have a nice steppy growled whistle, and SF-1 definitely has some sweet spots.
SF-1 works great as your normal type filter, but start self-patching and it really becomes something special. Raspy overdriven broke up howls, stuttery whistles…it works really well to carve out some dirty bass, and being able to use a bandpass filter to hone in on some small-range tones while going through both sides is akin to a dual peak filter; it made me start thinking about trying to get some dual peak action going on, so I put the Resonance high to both sides so that each would self-oscillate and then multed a sequence into both 1V/Oct inputs on SF-1 as well as my VCO [Expert Sleepers Lorelei] and tuned the Cutoff on both sides of SF-1 so that they were harmonically adjacent to what Lorelei was putting out. Patching in two outputs from Lorelei into each Input of SF-1 and with just one output on SF-1 I was able to get three distinct tones, one of which I tuned to a sub-octave of the main tone. It wasn’t quite chordal, there was no harmonic melding of the tones, but it sounded decent and was pretty interesting and usable.
Whether you utilize SF-1 as two filters for normal type duties or use it to sculpt your sound in more dramatic ways, you can’t lose with SF-1. I’m into this filter in a heavy way and I highly recommend it. Those extra outputs and the CV crossfade/pan circuit is a bullseye, and if this is the kind of stuff that “Precision” means, well then bring on more of it.

18 HP +12v 120mA -12v 120mA
Price: $350