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Schlappi Engineering Three Body

Eurorack Module By William Stokes
Published April 2024

Schlappi Engineering Three Body

A “phase and frequency modulation toolkit” is how Eric Schlappi describes the Three Body. Schlappi himself is an electronic musician dealing primarily in the world of noise (I myself am a proud owner of two of his cassettes), with his modules seemingly designed to facilitate his own craft as much as they are for others. A digital module with all the upfront goodness of an analogue interface, at its most basic level the Three Body is an array of three independent oscillators which can each output sine, triangle, saw and square waves, with the central, main oscillator adding 90‑degree phase‑shifted cosine and co‑saw waves on top. That’s a total of 14 separate outputs, and it has the same number of inputs, too.

Alongside conventional volt‑per‑octave CV inputs for each oscillator, there’s also a Transpose input that handles all three at once. Minimoog‑style triple‑oscillator massiveness, triad chords — it all sounds excellent and is incredibly quick to dial in. Atop this, the central oscillator’s out‑of‑phase waveforms are primed for lush stereo width. If the Three Body was sold as a classic oscillator then I dare say it would already do its job well. Things start to take off, however, with the involvement of its various switches and modes.

At 30HP it’s the largest module in the Schlappi range by some way. But considering what’s possible with it, the Three Body feels positively pint‑sized.

The Three Body behaves most like a conventional oscillator module when the three oscillators are in Free mode, where they operate independently of one another, and with their controls for FM Index, Phase CV and Phase Index on zero. Switch any or all into Ratio mode and move any of these knobs even modestly, and you will be catapulted into another sonic territory entirely. This is largely thanks to the fact that the Three Body operates in the realms of both phase and frequency modulation, which, for brevity, I’ll just say are closely related but not the same. The oscillators will harmonically track another signal patched to the sync input according to the ratio setting of the Mult and Div knobs (whose functions in Free mode constitute Coarse and Fine tuning respectively). An FM Mode switch toggles between linear and exponential settings, so it’s possible to track an incoming pitch accurately or, well, not so accurately. Last up is a Range switch which, ostensibly, influences the tuning range in Free mode and switches between multiplication or division of frequencies in Ratio mode.

I say ‘ostensibly,’ because there is simply a vast amount going on under the hood here, and I must resist the temptation to simply list combinations. You’d be hard pressed to fill a 25‑page manual with information about most standalone Eurorack oscillators, but here it’s as if Schlappi could easy have written a whole book about the Three Body. The manual usefully includes a generous amount of theoretical explanation of the difference between phase and frequency modulation, and a reference table for looking up all the possible switch combinations and what they each achieve. There are eight combinations, by the way, but that’s just for each oscillator, remember.

It’s ripe for internal patching, and there are some normalled connections as well; the sine wave of oscillator 3 is normalled to the Phase CV of oscillator 1, for instance, and the sine wave of oscillator 1 to the Phase CV of oscillator 3. Oscillator 2 has its two Phase Index inputs normalled to receive the sine waves of both its neighbours. So, editing anything on any one oscillator can have a potentially huge effect on the whole equation. It’s essentially the oscillator equivalent to holding two mirrors up to one another; I’m sure there’s an equation out there to calculate the total range of this thing, but rest assured you are unlikely to find its limit.

To best understand the Three Body from a basic level, I found that a good starting point was to dummy‑patch all the CV inputs, just to get some idea of what the hell was going on. It’s easy to forget that those normalled connections are just one means of operation. Replace even one with, well, anything, and the Three Body reinvents itself all over again. It’s as if every single move simply opens up more options.

Schlappi Engineering might just have made a modern classic.


It’s sometimes a good idea to disregard everything you’ve learned about synthesis, throw caution to the wind and start turning knobs with wild abandon. In many ways, you may as well throw all the theory out the window (or gratefully leave all the theory to Eric Schlappi) and just turn the Three Body on and start playing. I guarantee you’ll find a sound you like. Sure, manic knob‑twisting means that, at worst, things can descend into harsh and squelching generic FM noise, but in the spaces between there’s something exceptional here. At 30HP it’s the largest module in the Schlappi range by some way. But considering what’s possible with it, the Three Body feels positively pint‑sized. Schlappi Engineering might just have made a modern classic.