🎧 Audio Watermark Generator

Real-time embedded audio watermark generator and decoder built for STM32 microcontrollers.
This project implements a complete audio watermarking system capable of generating, embedding, and decoding digital identifiers in audio signals — designed for resource-constrained embedded environments.

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🚀 Overview

The system runs on an STM32G4 series microcontroller and transmits watermarks as ultrasonic FSK signals (typically around 21–22 kHz).
It includes:

• A configurable watermark bitstream generator
• Real-time audio modulation using FSK (frequency-shift keying)
• Timer-driven DAC output with circular DMA buffering
• Integration with an external DS3231 RTC for timestamping
• Metadata embedding: /STR…/DID…/LOC…/TMP…/TIM…/ format
• A Python decoder and analysis suite for validation and visualization

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🧠 Features

• ⚙️ Configurable parameters via user header file (user_config.h)
• 🕒 RTC integration (DS3231) with battery-backed clock
• 🧩 Preamble, silence, and polarity control via macros
• 🎚 Fixed-point DSP arithmetic for efficient modulation
• 🧮 FSK frequency pair definitions stored in frequency_pairs.h
• 🔄 DMA-driven continuous audio output (no blocking delays)
• 🧰 Python tools for decoding, spectrogram visualization, and testing

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🗂 Project Structure

Audio_Watermark_Generator/
├── STM32/                  # Embedded source (C, CubeMX, HAL)
│   ├── Core/
│   ├── Drivers/
│   ├── CMakeLists.txt
│   └── STM32G431XX_FLASH.ld
├── Python/                 # Decoder, analysis, and utilities
│   ├── demodulator.py
│   ├── decoder.py
│   └── utils/
├── .github/workflows/      # CI build workflows
└── README.md

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🧱 Build Instructions

🔹 Requirements

• STM32CubeIDE or CubeMX + CMake + Ninja
• GNU Arm Embedded Toolchain (13.3.1+st.9 or newer)
• OpenOCD / ST-Link V3 for flashing
• macOS, Linux, or Windows host

🔹 Build and Flash

cd STM32
cube-cmake -B build/Debug -S . -G Ninja -DCMAKE_BUILD_TYPE=Debug
cube-cmake --build build/Debug
openocd -f interface/stlink.cfg -f target/stm32g4x.cfg -c "program build/Debug/STM_TESTING.elf verify reset exit"

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🧩 Python Decoder (Optional)

A companion decoder written in Python can analyze captured watermarked audio files.

Run the decoder:

cd Python
python3 decoder.py input.wav

This script demodulates and extracts the embedded message from the audio signal.

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🧪 Current Status

This repository is under active development.
A macOS .app build (STM32Tool.app) is available as a beta release for easier build and flash automation.
👉 Download Beta Release

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👥 Contributors

• Kristian Gøystdal – Developer
• Einar Bergslid – Contributor

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📝 License

This project is released under the MIT License.
You’re free to use, modify, and distribute it for educational and research purposes.

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📡 Tags

stm32 · audio-watermarking · embedded-systems · signal-processing · dsp · c · c++ · real-time