If you remember my review of Schlappi Engineering’s Nibbler, you’ll have an idea of how impressed I was at the Pacific‑Northwest developer’s ability to take the seemingly banal language of binary and apply it in the most interesting of musical ways. I deemed that module a triumph. To recap: it uses four on‑or‑off stages — that is, 4‑bit — and essentially counts to and from 15, firing off correspondent gates as it does so. I’m reliably informed that a 4‑bit binary word is known as a ‘Nibble’, which is probably the cutest sentence you’ll read this issue. A slew of other features orbits this central function (not to mention a rather nice big Reset soft key), but at the heart of the Nibbler is the most fascinating and elegant concept of analogue‑does‑digital; something which I have only seen executed a handful of times and that I think presents a rich vein of creativity for developers.
Safe to say Eric Schlappi and crew are in the vanguard of this. The Nibbler isn’t the only binary‑based module in their range, which also includes the BTMX (‘bit mix’) and now the BTFLD (‘bit fold’), which is in front of me today. A slim little thing at just 6HP, on first glance the BTFLD looks like some kind of expander for the Nibbler, with a very similar‑looking set of outputs for its various binary values. It’s a very different beast, however: it’s a 4‑bit analogue‑to‑digital converter, processing any signal at its input with binary logic and mangling it in all sorts of wild ways. “The inspiration for this module,” explains Eric Schlappi, “is the similarity of binary encoding to wavefolding,” and this is essentially the BTFLD’s mantra: distortion, harmonic augmentation, sonic complexity, and everything else we love about wavefolding — but with a definite twist.
In a nutshell, feed the BTFLD a signal, audio or CV, and it will convert that signal into digital. Its Range switch selects between ±5V and +10V input and output ranges, the former generally better suited for audio and the latter for CV. It features variable gain at the input, controllable by hand as well as by CV, which is the primary tool for sculpting the harmonic character of audio and for offsetting control signals. A lovely little strip of LEDs in typical Schlappi blue smoothly displays the value of the input signal; a key visual cue next to the on/off LEDs of the other jacks. I’ve always been a fan of the generous amounts of visual cues on Schlappi modules, and the BTFLD is no exception.
A key difference between the BTFLD and the Nibbler is that the BTFLD’s ‘Bit’ outputs don’t just spit out gates; instead they output around 0.6V, 1.2V, 2.5V and 5V respectively, which is to say their values more or less double incrementally. They therefore behave somewhat differently according to what’s being fed into the module, most basically illustrated by the fact that if you send a simple, static waveform into the BTFLD, each output gives something resembling a different octave. The cumulative output of all of them is 10V, and they are recombined at the lowermost Stepped output into a 0‑10 V signal with 16 possible different values. For audio, this will output a type of bit‑crushed version of the input signal, while for a smooth LFO, for instance, it’ll introduce a sample rate and chop it into steps, as if fed through a clocked sample & hold. At audio rates the individual Bit outputs will spit out variously harmonically inaccurate distorted versions of the input signal with their different intervals and voltage values, while for the aforementioned LFOs they will pulse at particular intervals of the wave according to their resolution, making for a strange and highly creative sort of output‑switching sample & hold.
While many of the BTFLD’s sounds feel familiar, its design means it achieves them in a rather unique way.
The BTFLD’s I/O goes further still, with the topmost Saw output subtracting the stepped output from the input to essentially creating a wavefolder‑style, ‘sawtooth wave‑influenced’ version of the input signal, which was particularly fun when it came to audio, adding some serious edge and grit. On this note, I found the BTFLD got along very well with a low‑pass filter in the picture, just in case things got a little harsh at the top end. You’ll notice I’m using a lot of terms like ‘‑style’ and ‘type of’ — this is because while many of the BTFLD’s sounds feel familiar, its design means it achieves them in a rather unique way.
The last jack on the panel is Inject, which allows another signal to be added to the post‑VCA input signal for further modulation and signal mixing. This was an effective addition even as a means of combining two simple, asynchronous LFOs, which leads me to possibly my favourite thing about the BTFLD, which is that it isn’t just capable at processing either audio signals or low‑frequency modulation, it’s outstanding at both. As with most Schlappi Engineering modules, the theory behind the BTFLD is legion and very much deserving of a deep dive, but it’s also a helluva lot of fun to simply send it a signal and see what happens at different outputs.
Six unique outputs for one input in just 6HP is impressive. And all of them useful, too. I was able to take any input signal and endow it with various configurations of aliased, crushed harmonics, and then do things like pan them around the stereo field. This opened up a very interesting kind of ‘stereo‑widening distortion’ functionality, not to mention the opportunity to send different BTFLD outputs through different effects or processes around my system. In no time at all, more so with a little modulation in the picture, I was able to create huge, harmonically rich and aggressive sounds in stereo out of even the simplest input signal. Feeding it more complex audio, even field recordings, it works beautifully as a precise and characterful distortion effect, cramming as much harmonic information as possible — which isn’t much — through its outputs. Whatever you might have in your system, I can assure you it’s not quite like this. Schlappi Engineering are on a winning streak.