Amp modeler, multi FX.
Fully open source/hardware Teensy4 based guitar rig emulator including neural network based amp modeler, stereo IR cabsim and more.
TGX4 project aims at putting all the software work done for the Teensy DSP library into a practical pedal-form device delivering many interesting guitar and bass sounds, ready for jamming or recording. All design and firmware files are open source available in the project's github repository.
Project consists of two parts:
- Software, which can be compiled for and run on various Teensy4 based hardware platforms, the simplest being just a Teensy4 and the original Audio Adaptor Board.
- Hardware, a dedicated high quality audio DSP system designed specifically for use with guitar/bass instruments.
Features:
- 8 amplifier models,
- 10 cabinet impulse responses (7 guitar + 3 bass),
- Stereo enhancer for double track emulation,
- Compressor, Wah, Boost + Octave Up for input tone shaping,
- Noise gate,
- 3 band EQ + output highpass filter,
- 3 types of reverb (plate, spring, sci-fi),
- stereo ping pong delay with modualtion,
- 3 assignable pot inputs,
- Assignable expression pedal input,
- 128 presets stored on an SD card,
- 3.5" capacitive touch screen as user interface
- MIDI control,
- Web based (html page) MIDI control,
Software
Firmware is available as PlatofrmIO project for the Teensy4 board. The internal audio structrure is is shown below:
The components are partially mono, yet the bypass system for all of them runs in stereo. This way the effect can still be used as stereo Reverb/Delay after disabling the guitar amp related blocks.
Time based effect section consist of a reverb (one of three available models) and a delay run in parallel. Together with the infinite/freeze modes it delivers a wide range of ambient, looping type sounds.
User Interface
The easiest and quick way to access all the parameters is the WebMIDI based html control page. TGX4 exposes two intefaces when connected to the USB port: USB-MIDI and Serial (UART). The html control page is using the browser's built in Web-MIDI feature to control all the functions of the pedal with dials and buttons. The bottom part of the page is reseved for the serial console, showing status of the pedal or to access the command line interface.
Touch Screen
An optional, yet useful if the device will be used as stand alone unit is the GUI using a touch panel. For this task, a WT32SC01Plus board has been chosen providing a comfortable user experience with it's 480x320 px IPS display, parallel interface and capacitive touch screen, all driven by en ESP32-S3 microcontroller.
Communication between the audio DSP unit (Teensy4) and the Touch panel happens over an I2C bus.
Separate PlatformIO project for the ESP32 is provided in the github repository.
Target platforms
The main DSP firmware can be built for a few different available hardware platforms by chosing one of the predefined environments in the PlatfromIO project.
Platforms currently supported:
- HexeFX TGX4 dedicated hardware
- Teensy4.0 + Audio Adaptor Board (no PSRAM)
- Teensy4.1 + Audio Adaptor Board
- Teensy4.0 + Blackaddr TGA Pro (no PSRAM)
- Teensy4.1 + Blackaddr TGA Pro
Hardware
Guitar amplifier emulation, often involving very high gain and sharp filter processing requires a more specific approach to the hardware design. Testing many existing "consumer audio" solutions using integrated codec chips showed two main issues:
- Self oscillation at higher gain settings due to proximity of the input and output signals and signal coupling inside the codec chip.
- Noise level due to layout, power decoupling, lack of required signal buffers.
While the hardware platforms as Teensy Audio Board will work in this application, they will experience stated above issues wile using higher gain sounds.
To solve these problems a new, dedicated hardware platform has been designed with the focus on the following aspects:
- Low noise, high quality 32bit AD/DA convertes
- Separate AD (AK5552) and DA (AK4452) chips to maximize the separation between the input and output signals
- Option to replace the AD/DA converters with a new codec module
- Separate power rails for digital and analog circuit parts
- 4 layer PCB design
- Signal presence + clip indicator
- Buffered analog signal path, electronic bypass using NJFETs for their smooth switching transition
- Further expansion possible using two ribbon cable connectors (I2S2, SPI, I2C, GPIOs)
- GUI task handled by a separate ESP32-S3 board driving the display and capacitive touch panel
Controls:
- Up to 3 configurable potentiometers for quick parameter access
- Analog output volume control
- TRS expression pedal input
- 3 configurable footswitches
- Touch screen interface
Build instructions
Instuctions are provided in the GitHub repository.
Technical info (dedicated TGX4 hardware):
- 600MHz, Arm Cortex M7 DSP (Teensy4),
- 44.1kHz, 32 bit floating point processing,
- electronic, JFET based stereo bypass
- 1M input impedance,
- 470R output impedance,
- optional, analog dry signal path,
- 9V DC, 70mA power, regulated adapter only, DC5.5/2.1mm, center negative.
