A modular synthesizer application written in C, using SDL2 for graphics and audio, and supporting MIDI input via libremidi.

Live demo at: https://koppi.github.io/sdl2-synth

Features

• 4-oscillator synth: Each with independent waveform, pitch, detune, gain, phase, pulse width, and unison controls
• Mixer: Control the mix and master volume of each oscillator with bus compression
• Effects: Flanger, delay, reverb, and analog filter with real-time controls
• Arpeggiator: Multiple modes, adjustable tempo, octave control, and multi-octave chord arpeggiation
• Oscilloscope & Spectrum: Visualize output waveform and frequency spectrum
• MIDI input: Map MIDI CC to synth parameters for external control
• Interactive Keyboard: On-screen piano keyboard with visual feedback

Build Dependencies

• SDL2 (graphics, audio, events)
• SDL2_ttf (font rendering)
• Dear ImGui (GUI library)
• libremidi (MIDI input)

Build Instructions

Linux

sudo apt-get install git cmake ninja libsdl2-dev libsdl2-ttf-dev
git clone https://github.com/koppi/sdl2-synth && cd sdl2-synth
cmake --preset release
cmake --build --preset release && build/release/synth

macOS

brew install git ninja sdl2 sdl2_ttf
# Then build as above

Windows

Install SDL2, SDL2_ttf and libremidi development libraries, then build with MinGW or Visual Studio.

Running

build/release/synth

MIDI Control

MIDI input is mapped to numerous parameters (see src/midi.c for mapping). All GUI controls respond to mouse drag and mouse wheel. The oscilloscope is fed directly from the audio callback thread for real-time visualization.