disyn

Flues Disyn LV2 Plugin

This LV2 plugin is a direct port of the experiments/disyn distortion synthesizer. It provides 7 distortion synthesis algorithms in a monophonic LV2 instrument plugin.

Algorithms

The plugin features seven distortion-based synthesis algorithms, each with two parameters:

1. Dirichlet Pulse - Band-limited pulse via Dirichlet kernel

   • Param 1: Harmonics (1-64)
   • Param 2: Tilt (-3 to +15 dB/oct)

2. DSF Single-Sided - Moorer discrete summation formula

   • Param 1: Decay (0-0.98)
   • Param 2: Ratio (0.5-4)

3. DSF Double-Sided - Symmetric sideband generation

   • Param 1: Decay (0-0.96)
   • Param 2: Ratio (0.5-4.5)

4. Tanh Square - Hyperbolic tangent waveshaping (default)

   • Param 1: Drive (0.05-5)
   • Param 2: Trim (0.2-1.2)

5. Tanh Saw - Square-to-saw transformation

   • Param 1: Drive (0.05-4.5)
   • Param 2: Blend (0-1)

6. PAF - Phase-Aligned Formant oscillator

   • Param 1: Formant (0.5-6 ×f0)
   • Param 2: Bandwidth (50-3000 Hz)

7. Modified FM - Modified FM synthesis with exponential modulator

   • Param 1: Index (0.01-8)
   • Param 2: Ratio (0.25-6)

Signal Chain

MIDI Input → Voice Management → Algorithm Oscillator
  → Attack/Release Envelope → Schroeder Reverb → Master Gain → Audio Output

Building

Dependencies

• CMake (≥ 3.16)
• C++17 compiler
• LV2 development files

On Ubuntu/Debian:

sudo apt install build-essential cmake lv2-dev

Build Steps

cd lv2/disyn
cmake -S . -B build
cmake --build build

The DSP plugin (disyn.so) and metadata (manifest.ttl, disyn.ttl) are generated in build/.

Installing

Copy the bundle to your LV2 directory (commonly ~/.lv2 on Linux):

cmake --install build --prefix ~/.lv2

After installation, your LV2 path will contain:

~/.lv2/disyn.lv2/
├── manifest.ttl
├── disyn.ttl
└── disyn.so

Testing

Verify the plugin is recognized:

lv2ls | grep disyn
# Should output: https://danja.github.io/flues/plugins/disyn

lv2info https://danja.github.io/flues/plugins/disyn

Load in an LV2 host:

• Jalv: jalv.gtk https://danja.github.io/flues/plugins/disyn
• Ardour: Plugins → Instrument → Flues Disyn
• Carla: Add Plugin → Instrument → Flues Disyn

Parameters

Port	Name	Range	Default	Description
Algorithm	Algorithm	0-6	3 (Tanh Square)	Algorithm selector (enumeration)
Param 1	Parameter 1	0-1	0.55	Algorithm-specific parameter 1 (normalized)
Param 2	Parameter 2	0-1	0.5	Algorithm-specific parameter 2 (normalized)
Attack	Envelope Attack	0-1	0.5	Envelope attack time (0.001-1.0s)
Release	Envelope Release	0-1	0.5	Envelope release time (0.01-3.0s)
Size	Reverb Size	0-1	0.5	Reverb room size
Level	Reverb Level	0-1	0.3	Reverb wet/dry mix
Master	Master Gain	0-1	0.8	Output level

Note: Parameters 1 and 2 are normalized (0-1) and internally mapped to algorithm-specific ranges. The meaning changes based on the selected algorithm.

Usage

1. Load the plugin in your LV2 host
2. Connect MIDI input and audio output
3. Select an algorithm from the dropdown (default: Tanh Square)
4. Play MIDI notes (monophonic)
5. Adjust Param 1 and Param 2 to shape the sound
6. Tune envelope attack/release for desired articulation
7. Add reverb to taste

Architecture

The plugin follows the established pattern from lv2/pm-synth:

• Header-only modules in src/modules/
  • OscillatorModule.hpp - Seven algorithm implementations
  • EnvelopeModule.hpp - AR envelope generator
  • ReverbModule.hpp - Schroeder reverb (4 comb + 2 allpass)
• Main engine: DisynEngine.hpp - Coordinates modules, voice management
• Plugin glue: disyn_plugin.cpp - LV2 interface, MIDI handling
• Metadata: disyn.lv2/*.ttl - Port definitions, plugin metadata

Differences from JavaScript Version

The C++ port is a line-by-line translation of the JavaScript AudioWorklet code:

• Identical algorithms - Same math, same constants (TWO_PI, EPSILON)
• Identical parameter mapping - Same exponential/linear curves
• Identical signal flow - oscillator → envelope → reverb
• Sample-accurate MIDI - Events processed at exact sample positions
• Voice tail detection - Automatically stops processing when envelope finishes

Performance

• Real-time safe - No allocations in audio callback
• Low latency - Direct synthesis, no look-ahead
• CPU efficient - Optimized C++ with minimal overhead
• Monophonic - Single voice for low CPU usage

Known Limitations

• Monophonic only (no polyphony)
• No preset system (yet)
• No GUI (uses generic host controls)
• Parameter 1/2 labels don't change per algorithm (host limitation)

Future Enhancements

• Polyphony (4-8 voices with voice stealing)
• GTK3 UI with algorithm-specific parameter labels
• LV2 state extension for preset save/load
• Pitch bend support
• Modulation wheel → parameter mapping
• Per-algorithm parameter value displays

License

MIT License - See repository root for details.

See Also

• Source: experiments/disyn/ - JavaScript browser version
• Related: lv2/pm-synth/ - Physical modeling synth LV2 plugin
• Documentation: experiments/disyn/docs/DISYN-LV2.md - Implementation plan