A new Schlappi Engineering module is always an exciting proposition: There’s always something slightly unprecedented in Eric Schlappi’s modules, with a nice mix of the familiar and the edgy. It’s been awhile since Schlappi’s last module, 100 Grit, came out, so while we eagerly await the release of the Three Body, their triple digital FM/PM oscillator, Schlappi Engineering has now released Boundary, an OTA-based, all-analog multifunctional modulation/signal controlling module to tide us over for a bit. And that it does.
As with all Schlappi Engineering modules, there is more than meets the eye, and is sure to contribute to shaping, tweaking, warping, and of course, pulverizing your sound. Boundary is a little more subdued, subtle, and potentially elegant than previous Schlappi offerings, but it definitely fulfills promises and crosses boundaries.
Boundary is broken up into two parts; a cycling slew occupies the top half of the module, with a four quadrant multiplier [VCA] residing below that, with all ins and outs at the bottom of the module. In the SLEW portion of the module there are controls for the RISE and FALL, a CYCLE on/off toggle, and two CV controls; one that controls external incoming control voltage for the RISE, and one for the FALL, with inputs for each at the bottom. Both are normalled so that if no CV is patched in, the knobs shape the rise/fall respectively, with either logarithmic or exponential curve, something that is selectable for each via an INVERT toggle. If there is CV patched in, TOGGLE lets you invert the waveform for each the RISE and FALL. It’s really nice to be able to select curves for RISE/FALL separately as I always felt a bit constrained by modules that have both actions tied to one slope shape. It’s nice to rig up a long log curve on the attack with a snappy exponential on the fall, and with Boundary you can do that.
Rounding out the controls for the SLEW portion of Boundary, there are CV inputs for SLEW, which controls the rate of a bipolar input; RECTIFY, which flips the negative portion of the wave, turning it positive [useful for envelope following]; BOUND, for patching in an external envelope to use as a sort of VCA/threshold setting for the slew/envelope out; and TRIG, for triggering the SLEW/ENV. There’s also an EOR [end of rise] output for triggering an external event like a kick drum, gate, or foot massager or something. To each their own.
Boundary can be cycled slow for LFO use, or tweaked to get it fast enough to use as a sound source, using the RISE, BOUND, OR SLEW as a CV input—so long as the FALL is set low enough—though don’t expect perfect 1/v octave tracking. You can even use the EOR output as a sound source, as it puts out a square wave. However, I’ve got enough sound sources, and using Boundary as such, is—in my humble opinion—to completely miss the point of it, and borders on criminal misuse. Found at the top are also three blue LEDs that light up correspondingly with the outputted signal for a nice visual that can go from subtle-to-strobe-to-seizure.
The four-quadrant VCA section on Boundary is pretty simple; there’s a CV1/SLEW OUT control, that’s tied to the output of the SLEW section, with an accompanying INVERT toggle. There’s also a BIAS control with a RANGE toggle [+8V, +/-8V], and inputs for both CV controls, as well as an audio IN and OUT. This allows for a nice way to mix signals to get the perfect amount of effect. The four quadrants of the VCA allow for ring modulation, and there’s a built in limiter to control the more untamed signals a bit. It’s as if Schlappi is saying, “Go crazy. We’ve got you covered,” and it’s a very responsible addition for a Schlappi module, something that’s nuanced and could be easily taken for granted, but taming wild things is a deed too good to go unnoticed.
There are many things, many tricks that you can do with Boundary, rendering the term multifunctional almost a little too underwhelming to describe it. Ring modulation, delaying gate signals, frequency division, bouncing balls...Boundary does a lot, with a lot to explore.
Using the TRIG in as an attack/decay envelope generator, you can get some really unique wave shapes for modulation and it was here, right off the bat, that I lost hours of my life twisting and tweaking. It’s the details, the shifting of decay shapes, the slowing down of attack rates that captures my attention and my ear.
Patching into the SLEW can give portamento to your signal as well as create an attack/release envelope depending on how you have Boundary patched. This sort of utility module, while not as flashy as an overly illuminated sequencer, obese-knobbed filter, or mysteriously hieroglyphic’ed complex oscillator are actually my favorite modules to lose time to. It’s endless fun shaping envelopes, slewing notes, watching shapes mutate on an oscilloscope, and patching them into any/everything and listening to the changes. It feels scientific, like you’re changing the DNA sequence of a living creature or making the smallest incision possible with the sharpest stainless steel surgical knife ever. It’s the minutiae—that beloved minutiae—and Schlappi Engineering modules never skimp on that, always being good about the controls they offer, and how those controls operate in terms of feel and use.
Fully patched, and Boundary becomes a living, hard-breathing creature; at times, raspy, worn out, and tired from years of smoking menthols and working with paint thinner, and other times, slow, soft, self-entertaining, introspective, and whimsical. It might surprise you with pancakes for breakfast. It’s this duality that’s fun to explore, and I’m thinking of adding another to my rig, the way you get your dog a new dog friend, someone to chum around with. Having two of them [modules, not dogs], well that would push the boundaries of what they could do, into exponentially endless territory.

12 HP +12V 112mA -12V 59mA
Price: $219

schlappiengineering.com