thorn.audio splines eurorack visual vector curve module (Silver)

Splines is a visual vector curve generator in Eurorack format, with a wide frequency range and built-in quantizer, CV scope and CV processing capability. It can be used in ways similar to a wavetable VCO, LFO, step sequencer or envelope generator.

Onboard quantizer scales, backups and firmware updates are managed just as you would with an external USB drive. It's a small, shallow, multifaceted addition to any setup — and for touring rigs, it can fill many roles in exchange for very little space and weight.

In Depth

In the technical sense, "splines" are most commonly used in 3D modelling, animation and vector graphics. They're essentially a way of creating a curved path from one point to another.

In this module, you have up to sixteen user-configurable points, or nodes, which function much like a step sequencer, where the X axis represents time and the Y axis represents voltage. When the phase (time) reaches the X position of a node, the 1V/oct output changes to the Y position value of that node. Each of the sixteen nodes also has a configurable trigger setting, determining whether the gate output goes high when the phase crosses the X position of the node.

The nodes are connected by a spline, and the shape of this spline is determined by three parameters:

• Tension — changes how extreme the curve between the nodes is
• Continuity — sets the angle of the spline at the node
• Bias — shifts the tension to the left or right of the node

The spline output gives you a voltage following this curve. You can adjust which part of the full spline is output by changing the Zoom and Scroll parameters. The curve loops at the end, so when zoomed all the way out, the last node connects to the first.

The speed at which the phase progresses through the nodes can either be set fluidly using the "frequency" parameter, or quantized to fixed frequencies listed in .scl files in the "scales" directory on the module. Cycle frequencies range from 16 minutes per phase to 20kHz — from very slow LFO rates all the way up to the limits of hearing.

The output amplitude can be changed using the level parameter and CV input, allowing the module to be used without a dedicated VCA. When the spline shape goes higher or lower than the ±5V limits, a few different clipping options are provided, such as wavefolding or soft clipping — since all parameters can be overdriven substantially, this makes for some interesting effects.

The sync input is also configurable, letting you manage timing as you would a tap-tempo LFO, an envelope generator, or a step sequencer.

For working with control voltages, a basic rolling oscilloscope is available for each of the six CV inputs, including scaling and offset settings, so you can adapt the control voltage signal visually, directly in the module.

Developer resources such as drivers, templates, pin configs and best practices are also provided, in case you'd like to use the module as a development platform for your own ESP-32 based DSP projects. Firmware and quantizer scales can be updated easily by drag-and-drop via the front-accessible USB-C port.

Inputs/Outputs

• Output resolution: 1–16 bits
• Output sample rate: 192kHz
• Output voltage range: ±5V
• CV input resolution: 12 bits
• CV input sample rate: 1kHz
• CV voltage range: ±5V
• Trigger duration: 7ms
• Input trigger: 0–5V

Power

• +12V: 50mA/170mA
• -12V: 50mA
• 5V: 170mA/0mA (5V source switchable)

Dimensions

• Depth: 31mm
• Width: 10HP
• Height: 3U