🎛️ Real-Time Digital Effects Pedal

A modular, real-time audio effects system for Raspberry Pi, developed in modern C++ with multithreading, low-latency processing, and unit-tested DSP effect chains.

📜 Project Overview

The Real-Time Harmoniser is a standalone real-time embedded system designed to apply audio effects (like pitch-shifting and gain distortion) to incoming audio with minimal latency. The pedal is controllable via a hardware interface and written for the ENG5220: Real-Time Embedded Programming course.

Key Features:

• Modular DSP architecture with hot-swappable effect chains
• Sample-by-sample processing for minimal latency
• Real-time capable Harmonizer using SignalsmithStretch
• Multithreaded control-safe design with atomic buffer swapping
• CI-integrated Google Test unit testing
• Memory-safe code verified with Valgrind

🧩 System Architecture

+-----------+     +--------------+     +--------------------+
| Audio In  | --> | Sampling     | --> | DigitalSignalChain | --> Audio Out
+-----------+     +--------------+     +--------------------+
                                       |  Gain, Fuzz, Harmonizer ...
                                       +--------------------+

Each audio sample flows through a configurable DSP chain loaded dynamically from a config file.

⚙️ Getting Started

🔧 Prerequisites

• Raspberry Pi 4/5 (or any Linux system)
• libsndfile1-dev, libasound2-dev, libgtest-dev, valgrind
• CMake ≥ 3.7, Clang or GCC

🛠️ Build

chmod +x code/init.sh code/build.sh
./code/init.sh    # Installs dependencies and fetches submodules
./code/build.sh   # Builds the pedal and test binaries

▶️ Run

./code/run.sh     # Runs the real-time pedal binary

✅ Unit Tests

./code/unit_test.sh    # Runs unit tests with Valgrind

🧼 Clean

./code/clean_run.sh     # Re-builds the project and runs
./code/clean_test.sh    # Re-builds the project and runs the integration test

📂 Project Structure

code/
├── src/              # All source files
│   ├── dsp/          # DSP chain and factory
│   ├── effects/      # Harmonizer, Gain, Fuzz etc.
│   ├── sampling/     # Sample and output modules
│   └── test/         # Functional and unit tests
├── assets/           # Input/output WAV files and configs
├── CMakeLists.txt    # Project build configuration
├── run.sh            # Launches the pedal binary
├── test.sh           # Runs Valgrind test harness
└── init.sh           # Dependency setup and submodule fetch

📊 Performance

Metric	Value
Latency (per sample)	< 3μs (tested on x86)
Realtime Factor	~10x
CPU Usage	< 40% on RPi 4
Memory Leaks	❌ None beyond Alsa Standard (Valgrind verified)

🔬 Features Under Development

• Live web-based configuration via Angular UI (shred.local)
• Additional effects: Reverb, Delay
• Plugin support for 3rd-party effect modules

✅ Achievements

Criteria	Status
Multithreaded DSP	✅ Lock-free atomic switching
Realtime sample-by-sample	✅ Implemented in Harmonizer
Unit Testing	✅ GTest + Valgrind
CI/CD Integration	✅ GitHub Actions
Well-commented, structured code	✅ Reviewed and documented
Pedal UI and Config	✅ Completed

📜 License

MIT License. See LICENSE for details.