FINAL PROJECT CC1

FM Drone Synth (RNBO + C++ + Custom GUI)

Project Overview

This project is a simple FM drone synthesizer originally sketched in Max and exported to C++ using RNBO.
The exported DSP engine is integrated into a standalone application along with a custom graphical user interface.

The application runs as a standalone executable:

Executable:
RNBO App Example.exe

Repository

Full source code is available here:

👉 https://github.com/lenappss/rnbvst/

Project Architecture

The system consists of three main layers:

1. Synth Design (Max + RNBO)

  • The FM drone synth was prototyped inside Max using RNBO objects.
  • RNBO was used to export the patch as C++ source code.

Export output includes:

  • rnbo_source.cpp
  • RNBO runtime support files

2. Audio Engine (C++ / RNBO Export)

The core synth logic lives in:

rnbo_source.cpp

This file contains:

  • Generated DSP processing code
  • Parameter handling
  • Audio signal flow for the FM drone

It is automatically produced by RNBO whenever the patch is re-exported.

3. Custom GUI (C++)

A custom interface was written in C++ to control the drone synth.

GUI files:

DroneSynthGUI.cpp DroneSynthGUI.h

The GUI provides:

  • Control for FM parameters
  • Drone sound manipulation (ADSR)
  • Metro

Folder Structure (Key Parts)

export/ rnbo_source.cpp → RNBO-generated DSP engine

src/ Application source code

ui/ DroneSynthGUI.cpp DroneSynthGUI.h → Custom GUI implementation

build/ Contains compiled binaries

RNBO exports are placed inside the export/ directory and integrated into the application during build.

Build System

The project uses:

  • CMake for builds
  • RNBO C++ export for DSP
  • A C++ framework for audio and UI

Basic Build Steps

  1. Export RNBO patch into /export
  2. Run CMake:

cmake ..

  1. Build:

cmake –build .

The compiled executable will appear in:

build/RNBOApp_artefacts/

How It Works (Signal Flow)

Max Patch → RNBO Export → C++ DSP Engine → Application → GUI Controls

  1. The FM drone is designed in Max.
  2. RNBO converts the patch into C++ DSP code.
  3. The application hosts the DSP engine.
  4. The GUI sends parameter updates to the synth.

Features

  • Simple FM drone synthesis
  • Custom GUI controls
  • Standalone desktop application
  • Separation of DSP and UI logic

Notes

  • Any change in the Max patch requires re-exporting RNBO code.
  • GUI modifications do not require RNBO export.
  • The executable is intended as a standalone test application.

Possible Future Improvements

  • Preset management
  • MIDI support
  • Effects processing
  • Plugin build (VST3/AU)
  • Visual feedback (waveform/spectrum)