thorn.audio - Splines (Silver)

Splines is a visual vector curve generator for Eurorack — a module that turns drawn curves into voltages. The front panel makes the idea plain: a small window full of nodes and lines, a pair of encoders, a handful of buttons, and a very immediate concept — edit the shape you hear. From there it unfolds into an oscillator, LFO, envelope generator, step sequencer, quantizer, CV processor or scope, all built around the same idea: generate a curve, turn it into voltage, then bend it until it starts behaving in musically interesting ways.

The name is the concept; splines are curves drawn between points — common in vector graphics, animation and 3D modelling, but here repurposed for modular synthesis. You get up to 16 nodes, where the X axis is time and the Y axis is voltage. The module connects those nodes into a moving curve, and the Spline output follows that shape. Tension, Continuity and Bias control how the curve behaves between the nodes: sharper, smoother, leaning forward, pulling back, almost like editing motion in a visual tool, except the result comes out as CV or audio.

The visual side is a huge part of why Splines works so well. The display gives a direct view of what's happening: the curve, the nodes, the selected parameter, the resulting value, the incoming CV. It's sparse in controls but never cryptic — one encoder selects what you're editing, the other changes it, the buttons handle reset, pause and navigation. The screen obviously isn't here for decorative purposes; it's the module's logic made visible. Ear and eye meet in the same place, and it's a joy to work with :)

At slow rates Splines produces looping modulation, long evolving shapes, tap-tempo LFOs, stepped patterns, envelopes and odd little gesture curves. Clock it externally and it becomes a step sequencer with gates, triggers and per-node probability. Push it into audio range and it turns into a spline-based oscillator, with clipping, folding, wrapping, rectifying, comparator modes and bitcrushing on hand for rougher edges. The Level parameter and its CV input can stand in for a VCA — set Level to 0 and patch an envelope into Level CV to shape the output.

The quantizer is just as nicely thought through. Splines reads Scala .scl files over USB-C, so microtonal tunings are part of the picture from the start — drop the files onto its drive like you would on a USB stick, reboot, and they appear as a list of selectable scales. Quantization can apply to frequency or to voltages, the 1V/oct output works with the node values or forwards incoming pitch CV, and the built-in CV scope lets you see and scale incoming modulation directly on the module. Firmware updates, presets, backups and scala files are all handled over the same front USB-C port.

Splines is a multitool, but one with an interface so clear and a concept so unified that it never feels like switching between disconnected functions. Everything flows from the same idea of nodes, curves, time and voltage. All of these nice ideas come from Hallvard Kristiansen, who designed and built the module, with a beautiful UI and visuals by ASCII artist Joni Caparas. Since it does so much, the excellent manual is well worth a thorough read-through. Splines can be a precise utility, a strange oscillator, a microtonal quantizer, a modulation drawing machine or a small lab instrument for understanding what your rack is doing. It covers a lot of ground, but remains easy to operate, an intuitive and deeply flexible module that keeps finding new ways to be useful.

Features:

• Visual vector curve generator
• Up to 16 user-configurable nodes (X = time, Y = voltage)
• Spline shape controlled by Tension, Continuity and Bias
• Zoom and Scroll for selecting the output segment of the spline; curve loops at the ends
• Frequency range: 0.001 Hz (~16 minutes per cycle) to 20 kHz
• Functions as wavetable VCO, LFO, step sequencer, envelope generator, quantizer or CV scope
• Per-node trigger settings (off / trigger / gate) with adjustable per-node probability
• Built-in quantizer with .scl (Scala) file support, drag-and-drop via USB (Maximum of 30-40 files recommended)
• Quantizer can apply to phase frequency, output voltages or the 1V/oct input independently
• Six CV inputs, each with its own oscilloscope, gain (±2.0x) and offset (±5V)
• Sync input with modes for looping, reset phase, tap tempo, step, external clock, sample & hold
• Level parameter and CV input can function as a built-in VCA — no external VCA required
• Clipping modes: Hard, Soft, Fold, Wrap, Rectify, Comparator
• Bitcrush from 16-bit down to 1-bit
• Configurable 1V/oct output: nodes only, forwarded input (optionally quantized), or both summed
• Two encoders with push function; three mechanical Kailh Choc V2 low-profile keyswitches (hot-swappable)
• 1.83" color LCD (284 × 240) over SPI; configurable UI color, brightness and orientation
• Front-accessible USB-C for drag-and-drop firmware updates, presets, scales and backups
• Preset system with save, load, rename, update, delete and factory reset
• ESP32-S3 processor (WiFi and Bluetooth available for developer use)
• Open development platform with templates, drivers and pin configs on GitHub
• Output: 1–16 bits resolution, 192 kHz sample rate, ±5 V range
• CV input: 12 bits, 1 kHz sample rate, ±5 V range, protected by clipping diodes
• Trigger duration: 7 ms; sync-to-output latency approx. 2 ms
• Switchable internal/external 5V power source via rear jumper
• Concept and design by Hallvard Kristiansen, UI design by Joni Caparas