Schlappi Engineering LLC - Boundary Layer (Black)

The Boundary Layer is a formidable modulation hub, designed in the grand tradition of function generators like the Serge DUSG and Make Noise Maths, yet it carves out its own unique space. Already the original Boundary module from Schlappi impressed us, so we were quite keen to see this larger follow-up. It comes with three independent channels, each ready to act as a cycling LFO, a snappy AD/AR envelope, a portamento-style slew, or even a simple low-pass filter. This versatile three-channel design makes it an incredibly dense and useful utility for many different types of racks.

The build quality is exactly what we've come to expect from Schlappi in the past—solid components, nothing wobbly, and overall excellent sturdy construction. One really interesting aspect of this module is the interaction between its three channels. Global "ALL" inputs allow you to drive all three channels from a single source, creating complex but musically related movements. There's also a special BOUND input, which lets you achieve unusual rhythmic effects like a "bouncing ball" envelope for instance, or you can use it as a pseudo-VCA. The MAX, MID, and MIN outputs aren't just for mixing; they're an analog logic section that constantly sorts the three channel voltages, providing an interesting way to waveshape, create new complex modulations, or generate wide stereo images.

Like many of the famous function generators that came before it, Boundary Layer has a pretty long list of use-cases — experimentation is key (or you simply go about it the RTFM way). It can handle all the standard duties of envelopes and LFOs flawlessly, but its true character is revealed when you start cross-patching its sections. It's a system for generating intricate, interwoven signals that feel dynamic and alive—a proper centerpiece for anyone who loves to explore the possibilities of modulation.

Features:

• Triple cycling slew/function generator
• Each channel can function as an LFO, AD/AR Envelope, Voltage Controlled Slew, or Low-Pass Filter
• Independent controls for Rise and Fall times with CV inputs
• Continuously variable envelope shape from logarithmic to exponential
• TRIG input for Attack/Decay (AD) envelopes
• SLEW input for Attack/Release (AR) envelopes, portamento, or filtering
• BOUND input for dynamic amplitude/frequency effects and "bouncing ball" rhythms
• Global "ALL" inputs for TRIG, CV, and SLEW to control all three channels simultaneously
• MAX, MID, and MIN analog logic outputs for complex waveshaping and stereo effects
• End-of-Cycle (EOC) gate output, jumper-selectable on the rear between End-of-Rise (EOR) and End-of-Fall (EOF)
• A rear header allows switching the MIN output to a standard MIX output