Antidote audio board

Budget neural amp modelling on a Radxa Cubie A7Z.

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(sloppy demo video)

What this project does

Neural Amp Modeler (NAM) uses neural networks to model guitar amplifiers from recorded input/output pairs, then reproduces their response on live guitar audio. I want to make a standalone guitar pedal for it.

Rust firmware runs on a Radxa Cubie A7Z Linux SBC. It manages real-time audio capture and playback, including the hot loop that processes each buffer, wraps NAM A2’s C++ DSP library via FFI, and coordinates model loading and the pedal’s peripherals. A custom audio board provides instrument-level input and output.

The end goal is a budget, performant, standalone NAM pedal targetting buffers processed in under 10 ms (ideally under 5 ms) - essentially the threshold for human auditory latency perception.

This repo

• src/: Rust firmware for audio processing, NAM A2 FFI, model loading, and pedal controls.
• hardware/: Schematics and PCB design files for the audio board + associated Linux device tree overlays

Please see this repository as more of a reference design for what's possible and how such a pedal could be built, rather than a polished product.

Hardware setup

1. Source a Radxa Cubie A7Z
   • Note: other similar SBCs (like the Pi Zero/OrangePis/etc.) likely will not work due to different GPIO header pinouts
2. Have the audio board fabricated with all components populated.
3. Connect the audio board to the SBC via the 40-pin GPIO header.
4. Connect other peripherals to the audio board. In my case, I connected (and built my firmware around):
   • 3.5mm headphone jack for phones
   • 6.35mm TS input for guitar
   • 6.35mm TS output for amp
   • A single footswitch
   • An I2C OLED display (SH1106)
   • A WS2812B LED strip

Firmware setup

1. Flash the SBC with Linux. Official Radxa images or community Armbian images should work fine.

2. Compile and load the driver for the audio board's codec (TAC5112).

   • See the TI git repository for the source. Check out a branch or tag compatible with your kernel version.
   • Run make, then load the kernel module with insmod or modprobe.

3. Compile and load the device tree overlay for the audio board.

   • The source is ./hardware/tac5112_i2c_i2s_overlay.dts. Compile it with dtc into a .dtbo file, then load it via rsetup.

4. Configure the codec's ADC, DAC, and capture/playback paths if needed. These commands may be needed:

   sudo amixer -c 0 cset name='ASI_RX_CH1_EN Switch' on
   sudo amixer -c 0 cset name='OUT1x Source' 'DAC Input'
   sudo amixer -c 0 cset name='OUT1x Config' 'Pseudo differential with OUTxM as VCOM'
   sudo amixer -c 0 cset name='OUT1x Driver' 'Headphone'
   
   sudo amixer -c 0 cset name='ASI_RX_CH2_EN Switch' on
   sudo amixer -c 0 cset name='OUT2x Source' 'DAC Input'
   sudo amixer -c 0 cset name='OUT2x Config' 'Mono Single-ended at OUTxP only'
   sudo amixer -c 0 cset name='OUT2x Driver' 'Line-out'
   
   sudo amixer -c 0 cset name='ADC1 Config' 'Single-ended'
   sudo amixer -c 0 cset name='ADC1 Common-mode Tolerance' 'AC Coupled with 100mVpp'
   sudo amixer -c 0 cset name='ADC1 Full-Scale' '2/10-VRMS'
   sudo amixer -c 0 cset name='ASI_TX_CH1 Slot' 'Slot0'
   sudo amixer -c 0 cset name='ASI_TX_CH1_EN Capture Switch' on
   sudo amixer -c 0 cset name='ADC1 Digital Capture Volume' 161
   
   sudo amixer -c 0 cset name='IN1 Source Mux' 'Analog'
   sudo amixer -c 0 cset name='IN2 Source Mux' 'Analog'

5. Pull in the dependencies, then build the firmware in release mode on the SBC or cross-compile it on a host:

   git submodule update --init --recursive
   cargo build --release

6. Run the firmware in release mode, passing the directory containing your .nam models. If omitted, it uses resources/:

   ./target/release/antidote /path/to/nam/files
   # Or:
   cargo run --release -- /path/to/nam/files

   2026-09-25T16:57:33.860341Z  INFO antidote: Starting Antidote.
   2026-09-25T16:57:33.880659Z  INFO antidote::modeller: Loaded NAM A2 model. model_path=resources/fender_brown.nam
   2026-09-25T16:57:33.880875Z  INFO antidote: Starting CPAL.
   2026-09-25T16:57:33.989547Z  INFO antidote: Playing back audio for 500 seconds.
   2026-09-25T16:57:34.898597Z  INFO antidote::audio: Audio errors input_drops=0 output_drops=0 output_underruns=320
   2026-09-25T16:57:35.898842Z  INFO antidote::audio: Audio errors input_drops=0 output_drops=0 output_underruns=320
   2026-09-25T16:57:36.899102Z  INFO antidote::audio: Audio errors input_drops=0 output_drops=0 output_underruns=320
   ...

Polishing touches

Once everything is working, some things you can do to make the pedal more usable:

• Add a systemd service to run the firmware on boot

Optimizations

• Disable all unnecessary kernel modules to reduce boot time
  • Stock boots in around ~20 seconds which is actually pretty good - but you can cut another 5-10
• If using a 6.12+ kernel, you can use the play with the PREEMPT_RT to reduce latency
• Play around with mlockall and threadirqs, core pinning/isolation. You can push buffer sizes to around ~24 this way yielding a theorical round-trip latency of ~2ms.

Some design goals/notes:

In principle, this project actually builds an entire hardware platform for any real-time guitar processing application for Linux SBCs. You can just as easily swap out the the firmware for another that runs say LV2/VST plugins. Though the main focus for this project is a standalone NAM pedal.

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Built on top of:

• NAM A2 Source Code
• NAM A2 Reference