MonkSynth

A monophonic vocal synthesizer that sounds like a monk chanting. Built using formant-wave-function (FOF) synthesis, inspired by the classic Delay Lama VST plugin by AudioNerdz (2002).

Download the latest release — available for Windows, macOS, and Linux.

MonkSynth v0.0.1-beta.1 in Ableton Live 12, with the classic theme imported from the original Delay Lama DLL

Features

• FOF synthesis engine producing realistic vocal formants
• XY pad for real-time pitch and vowel control
• Built-in stereo delay effect
• MIDI support: note on/off, pitch wheel, CC1 (vibrato), CC5 (glide), CC7 (volume), CC12 (delay), CC13 (voice)
• Automatable Pitch Bend parameter (±12 semitones). The hardware pitch wheel is routable to either Vowel (Classic / Delay Lama compat, the default) or Pitch via right-click → Pitch Bend
• ADSR envelope with configurable attack, decay, sustain, release
• Unison mode with up to 10 detuned voices and voice spread
• Theme system with right-click context menu for custom themes
• Import classic theme from the original Delay Lama DLL
• 5 factory presets
• VST3 plugin format (Windows, macOS, Linux) and Audio Unit (macOS)

Building

Prerequisites

• CMake 3.20+
• C/C++ compiler (MSVC, GCC, or Clang)

Build

cd cpp
cmake -B build
cmake --build build --config Release --target MonkSynth

The VST3 SDK is fetched automatically by CMake. The built plugin is placed in your system VST3 directory.

macOS Audio Unit

To also build the AU plugin, install the AudioUnit SDK and configure with:

cmake -B build -G Xcode -DSMTG_AUDIOUNIT_SDK_PATH=/path/to/AudioUnitSDK
cmake --build build --config Release --target MonkSynth-au

DSP unit tests

The pure-C DSP layer (dsp/) has a small unit test suite exercising ADSR envelope boundaries, the note stack, unison detune math, pitch-bend propagation, and delay-line feedback stability. Tests are opt-in so they don't affect normal plugin builds:

cd cpp
cmake -B build-tests -DMONKSYNTH_BUILD_TESTS=ON
cmake --build build-tests --config Release
ctest --test-dir build-tests --output-on-failure

CI runs the test suite on the Linux job before packaging each release, so any DSP regression blocks the build.

Installation

• macOS: Run the .pkg installer — installs both VST3 and AU plugins
• Windows: Run the .exe installer — installs the VST3 plugin
• Linux: Extract and copy MonkSynth.vst3 to ~/.vst3/

Themes

MonkSynth ships without a built-in theme. On first launch, it shows a setup screen where you can import the classic look from the original Delay Lama DLL (available as freeware from audionerdz.nl).

You can also load custom themes via right-click on the plugin GUI. A theme folder contains a theme.json manifest and any combination of these PNG files (missing ones fall back to 1x1 placeholders):

• background.png — main background (360x510)
• monk-strip.png — animation sprite sheet (5x6 grid, 311x311 frames)
• knob-left.png / knob-right.png — rotary knob filmstrips (50x3000, 60 frames)
• fader-down-large.png / fader-down-sm.png / fader-right-sm.png — fader handles
• info.png — info overlay (253x275)

Looking for fresh default themes to ship with the plugin. If you design a theme you're proud of, open a PR — I'd love to include contributed themes in the next release. The right-click menu has an "Open Themes Folder" item that reveals where themes live on disk.

Translations

The plugin UI (setup screen, info overlay, right-click menu, and DLL-importer error messages) is available in English, Japanese, and Korean. The language auto-detects from your OS locale; you can override it via right-click → Language.

Japanese and Korean translations were generated by a large language model as a starting point. Native-speaker contributions are very welcome — please open a PR editing cpp/src/strings_ja.h or cpp/src/strings_ko.h. Every string is indexed by the StringId enum in cpp/src/i18n.h; keep entries in the same order and leave any you're unsure about as empty strings to fall back to English.

Parameter names (shown in your DAW's automation lanes) stay English on purpose — tutorials, presets, and community discussion all assume the English names.

Acknowledgments

• Delay Lama by AudioNerdz (2002) — the beloved freeware VST plugin that inspired this project
• Xavier Rodet (IRCAM) — formant-wave-function (FOF) synthesis technique
• stb_image_write by Sean Barrett — single-header image writing (MIT / public domain)
• VST3 SDK by Steinberg — plugin framework (MIT)

License

MIT