The Infinity System

Infinity is a multichannel system with true polyphonic sustain. Polyphonic sustain means that all vibrating strings will sustain indefinitely until muted. You can play single notes, layered harmonies, counterpoint, or chords that sustain forever.

The system integrates the Nu Multi multichannel pickup and sustain drivers using multiple feedback loops, orchestrated by a microprocessor that manages the precise interplay between the pickups, strings, and the drivers.

Each string forms a closed feedback loop consisting of a pickup, a driver, and a controller that manages the energy fed back to the string and balances the drive across the strings so that no single string overpowers the others. The string acts as a resonant filter that only responds to its fundamental frequency and its harmonics. Positive feedback drives it into oscillation, and the controller adjusts feedback gain to maintain even sustain and output across all strings.

Multichannel

The Nu Multi pickups are designed for multichannel effects processing—one for each string (distortion, EQ, compressor, delay, pan, pitch-shift, etc.). Such extensive processing is now possible due to advances in digital signal processing and the proliferation of multichannel audio interfaces and multi-track audio software. The Nu Multi can also be installed alongside traditional monophonic pickups, giving you both polyphonic and conventional outputs in the same instrument.

Multichannel output together with multichannel sustain opens a vast horizon of sonic possibilities that were not possible with traditional monophonic guitar setups, including effect chains and amplifiers.

The short demo video below has sustain control set to roughly 5. The audio from the pickups is captured and mixed as raw as possible. There are no effects except for a touch of reverb, and the Ascend VPU is inserted in each channel, used solely for noise reduction with the virtual pickups bypassed. There is no EQ and no compression.

Design Philosophy

Sustain first, tone shaping later.

Infinity is not an aggressive sustainer. The goal is a neutral platform that preserves pick attack and the instrument’s natural character. The sustain controller’s sole function is to manage per-string feedback and maintain balance across strings at any fret or volume level. In most cases, a sustain setting of 4–7 is adequate.

There are no complex dynamics and timbre manipulations in the guitar itself. The system adds energy to the strings without modifying timbre.

The rationale is that you can utilize post-processing with a DAW or external effects hardware much more effectively to shape the envelope and timbre. Post effects processing handles the heavy lifting, including compression, dynamic ADSR envelope shaping for volume and tone, and overdrive or distortion, as well as synthesis. All of these happen after the sustain stage.

Following this rationale, there is no “harmonic mode,” unlike many traditional sustainers. The goal is a clean, sustained fundamental with minimal harmonic shift across all strings and fret positions. We want a natural sound with no audible processing artifacts. Harmonic effects, and much more, are better achieved with downstream synthesis and processing.

The image below shows the actual raw envelope of the short demo above. It is easy to see how this envelope can be shaped using post-processing by adjusting the attack and sustain levels to suit. What matters is that the strings continue sustaining indefinitely until you release them.

Here are two experiments in sustain and tone. Sonic Envelopes explores clean, evolving textures. Poly Fuzz dives into per-string distortion. Both show what is possible with polyphonic sustain when each string has its own voice.

In Sonic Envelopes, short audio snippets were recorded using only the Thor Infinity guitar to demonstrate polyphonic sustain and multichannel processing. No synths, no drums, no bass, and no overdubs. The raw guitar, tracked per string, was processed in Logic Pro using various audio effects plug-ins. The goal was to morph the sustained signal into new textures through post-processing. A typical multichannel signal flow was outlined: per-string preprocessing, per-string inserts and sends, then a poly mix bus for final glue.

This second part, Poly Fuzz, explores polyphonic distortion. Traditional distortion extends sustain and changes timbre by adding harmonics, but with multichannel sustain the first role is already covered. Timbre can be shaped in other ways, so distortion becomes just one of many waveshaping tools.

The Hardware

The system has a small footprint, the size of a PAF humbucker. The output amplifier drives two coils: one for the treble side and one for the bass side. Thinner strings require more power to drive into oscillation due to lower magnetic mass. The treble driver coil takes care of the plain strings for up to three strings. The system is capable of up to 8 strings. The bass driver coil can drive three to five wound strings, using a suitably sized driver coil. The microcontroller balances the output drive across all strings to maintain smooth and even output levels via feedback from a Nu-Multi multichannel pickup.

Core Architecture

The Infinity system is kept as simple as possible. There is a single sustain control via control voltage (CV) that determines the sustain level. Normally, the sustain level is controlled by a CV potentiometer. But since it’s just a control voltage, the system can also be controlled externally, e.g., via an expression pedal, for hands-free operation.

Block Diagram

Modules

The Infinity system is composed of three modules that snap together vertically to maintain a small footprint.

  1. The Driver module (rightmost board in the picture below) contains the amplifiers for driving the coils. These are linear class AB amplifiers specifically chosen to deliver clean, noise-free output.
  2. The MCU module (middle board in the picture below) contains the microcontroller, which includes provisions for flashing the firmware via USB.
  3. The Main module (leftmost board in the picture below) integrates the MCU module and the Driver module and connects them to controls and the Cycfi standard 19-pin output jack.