NeuralPi

NeuralPi is a guitar pedal using neural networks to emulate real amps and pedals on a Raspberry Pi 4. The NeuralPi software is a VST3 plugin built with JUCE, which can be run as a normal audio plugin or cross-compiled to run on the Raspberry Pi 4 with Elk Audio OS. NeuralPi is intended as a bare-bones plugin to build on. The pedal runs high quality amp/pedal models on an economical DIY setup, costing around $120 for hardware to build yourself.
Check out a video demo on YouTube
Check out the step by step build guide published on Towards Data Science

NeuralPi can sound like an amplifier or distortion/overdrive pedal using the power of neural networks. Models trained from recordings of real amps and pedals can be loaded into the plugin for endless possiblities on your guitar. Create your own models or use custom tones from GuitarML.

There are four main components to the guitar pedal:

This is the normal VST3 plugin, which can be compiled for Windows/Mac/Linux using JUCE. It includes a model import feature, dropdown menu, and gain/level controls. The plugin compiled for Elk Audio OS is headless, meaning there is no GUI.

Installing the plugin

For the cross-compiled Raspberry Pi / Elk Audio OS compatible VST3 plugin, download here.

WARNING: The audio output of the NeuralPi is at line level. Guitar amplifiers expect a low level electric guitar signal (instrument level). When using the NeuralPi with a guitar amp, start with the master volume at 0 and SLOWLY increase from there.

Changing Models

The NeuralPi running on Elk will load one model per instance of the plugin. By default this is the "bj_model_best.json" file. Model select controls will be added in the future, but for now you must overwrite this file to load different models. On Elk Audio OS, the models will be installed here after running the plugin for the first time:

/home/mind/.config/JUCE/NeuralPi/tones

Backup the Blues Junior amp model with this:

cp bj_model_best.json bj_backup.json

And overwrite the original model to try a new one:

cp ts9_model_best.json bj_model_best.json

If you need to revert back to the original state, remove the /tones folder and restart the plugin. The "bj_model_best.json" is a Fender Blues Jr. amplifier at full gain, and the "ts9_model_best.json" is the Ibanez TS9 overdrive pedal at full drive.

To Do

Currently, the NeuralPi plugin running on Elk OS has no user controls. It runs a single model that can be swapped out before running the plugin. The next step is to add user controls via OSC messages, so that a remote instance of the plugin can control the NeuralPi over Wifi. These controls will include Gain/Volume, EQ, and model selection.

Elk Audio OS also supports physical controls through Sensei. Gain/Volume and EQ knobs can be added, as well as a LCD screen for selecting different models. One could build an actual guitar pedal with NeuralPi and any number of other digital effects and controls.

While running PyTorch locally on the Raspberry Pi might be a stretch, it is fully capable of recording high quality audio with the HiFiBerry hat. Implement a capture feature by automating the recording of input/output samples, pushing to remote computer for training, then updating the Pi with the newly trained model.

Info

The neural network is a re-creation of the LSTM inference model from Real-Time Guitar Amplifier Emulation with Deep Learning

The Automated-GuitarAmpModelling project was used to train the .json models.
IMPORTANT: When training models for NeuralPi, ensure that a LSTM size of 20 is used. NeuralPi is optimized to run models of this size, and other sizes are not currently compatible.

The plugin uses RTNeural, which is a highly optimized neural net inference engine intended for audio applications.

The HiFiBerry DAC+ADC card used for this project provides 192kHz/24bit Analog-to-Digital and Digital to Analog, which is industry standard for high quality audio devices. The plugin processes at 44.1kHz (specified in config file) for the neural net DSP.

Build Instructions

To build the plugin for use on the Raspberry Pi with Elk Audio OS, see the official Elk Audio Documentation

To build for Windows/Mac/Linux:

Clone or download this repository.
Download and install JUCE This project uses the "Projucer" application from the JUCE website.
Download the RTNeural submodule (cd into the NeuralPi repo first):

git submodule update --remote --recursive
Download and extract: json Json for c++.
Open the Chameleon.jucer file and in the appropriate Exporter Header Search Path field, enter the appropriate include paths. For example:

  <full-path-to>/json-develop/include
  <full-path-to>/NeuralPi/modules/RTNeural
  <full-path-to>/NeuralPi/modules/RTNeural/modules/xsimd/include

Build Chameleon from the Juce Projucer application for the intended build target.

Note: Make sure to build in Release mode unless actually debugging. Debug mode will not keep up with real time playing.