Latest stable release:

macOS ARM/Intel 3.1.0
Windows x64 3.1.0
Windows x86 3.0.0
Linux was supported as of 1.0.8. It has regressed since, but shouldn't be super-hard to get working again. No binary was ever distributed; It has only ever been build-from-source.
- The new CMake build system may work on Linux already; give it a try
- Refer to the Win32 cross-compile Dockerfile to understand the steps required to run CMake

Demo track: mp3, FLAC, FLAC +Soundgoodizer

What

juicysfplugin is a cross-platform audio plugin for playing MIDI music through a soundfont synthesizer.

It's well-suited for making videogame music. If you have a soundfont of your favourite game, you can write your own melodies with its instruments.

JUCE is the framework for making audio plugins.
fluidsynth is the soundfont synthesizer.

Supports SF2 and SF3 soundfont formats.

Supports the following MIDI events:

noteon, noteoff
192 program change (this changes soundfont preset)
pitch wheel
aftertouch (key pressure)
channel pressure
default modulators as described in SoundFont specification 2.4
- includes (among others): CC 1 modulation wheel is mapped to vibrato LFO pitch depth
CC 71 Timbre/Harmonic Intensity (filter resonance)
CC 72 Release time
CC 73 Attack time
CC 74 Brightness (cutoff frequency, FILTERFC)
CC 75 Decay Time
CC 79 undefined (being used as Sustain time)
may support SysEx (untested)

Mode 1: standalone application

juicysfplugin.app (or .exe on Windows) is a standalone application, for playing around.

You can plugin your hardware MIDI keyboard, or play with the software MIDI keyboard. Or route MIDI messages into it from a virtual MIDI controller (e.g. the macOS IAC Bus).

Mode 2: audio plugin

juicysfplugin audio plugins are provided: VST, VST3, AU, AUv3.
This means you can host it inside your DAW (e.g. GarageBand, FL Studio Mac, Sibelius…) to record the sounds you make.

Why

I couldn't find a free, easy-to-use macOS audio plugin for making music with soundfonts.

Install (macOS)

Latest release: https://github.com/Birch-san/juicysfplugin/releases

Download Release.tar.xz, open it to unzip.

Release contains:

juicysfplugin.app  # standalone application, for playing around
juicysfplugin.component  # AU plugin
juicysfplugin.vst  # VST plugin
juicysfplugin.vst3  # VST3 plugin

To install plugins, move them to the following folder:

juicysfplugin.component -> ~/Library/Audio/Plug-Ins/Components/juicysfplugin.component
juicysfplugin.vst -> ~/Library/Audio/Plug-Ins/VST/juicysfplugin.vst
juicysfplugin.vst3 -> ~/Library/Audio/Plug-Ins/VST3/juicysfplugin.vst3

Launch (macOS)

Now, you may do one of the following:

Open the standalone juicysfplugin.app
Load the AU/VST/VST3 into your favourite DAW (e.g. GarageBand, FL Studio)

Usage

You must drag-and-drop a soundfont into the file picker.

Here's some soundfonts to get you started:

Fatboy (no specific license stated, but described as "free")
MuseScore's recommended soundfonts (includes MIT, GPL, other licenses)
FlameStudios' GPL-licensed guitar soundfonts

I'll refrain from recommending certain General MIDI or videogame soundfonts, since the licensing and provenance are often unclear.

Keybindings

Gain keyboard focus by clicking the plugin's keyboard.

Up-down arrow keys to switch preset.
Left-right to switch bank.

ASCII -> MIDI keybinding is the same as FL Studio's:

Using the standalone .app (macOS) / .exe (Windows)

Generally the .app will Just Work™, but if your audio setup is more bespoke, then you'll need to configure.

Options > Audio/MIDI settings

Set Output to Built-In Output

Or any output device that you can hear audio through.

Building from source (macOS)

Install XCode and XCode command line tools. Accept terms.

Install JUCE 5.3 in /Applications.
We expect to find JUCE headers in /Applications/JUCE/modules.

(Optional) To target VST3, install Steinberg VST3 Audio Plug-Ins SDK.
We expect to find a folder ~/SDKs/VST_SDK/VST3_SDK.

(Optional) Install IntelliJ AppCode if you prefer it to XCode.

Open juicysfplugin/Builds/MacOSX/juicysfplugin.xcodeproj in XCode (or IntelliJ AppCode).

Build & run the "juicysfplugin - Standalone Plugin" target.

All the libs we link against are project-local (see juicysfplugin/Builds/MacOSX/lib_relinked).
I have used install_name_tool to give these libs relative install names. This ensures that any product you build will be portable.

See my blog post for a deeper explanation as to how juicysfplugin is linked for portable distribution on macOS.

Testing VST/AU plugins inside an audio plugin host

You'll notice that the schemes for [VST, VST3, AU, AUv3] targets are configured such that "Run" launches the executable AudioPluginHost.app. This lets you run the audio plugin as though it were hosted inside a DAW.

I recommend building (e.g. with XCode) the simple Audio Plugin Host that comes with JUCE Framework:

/Applications/JUCE/extras/AudioPluginHost/Builds/MacOSX/AudioPluginHost.xcodeproj

Then symlink /Applications/JUCE/AudioPluginHost.app to the built AudioPluginHost.app (because that's where I told the Run configuration to look for AudioPluginHost.app):

ln -sf /Applications/JUCE/extras/AudioPluginHost/Builds/MacOSX/build/Debug/AudioPluginHost.app /Applications/JUCE/AudioPluginHost.app

Visual Studio Code settings

Concerning the use of Visual Studio Code extension, C/C++ for Visual Studio Code, as an IDE (i.e. instead of XCode)…

Following advice is for macOS, using brew-installed LLVM 8 Clang.

All includePath entries are shallow (no recursive globbing) for now, since I don't have any deeply-nested headers.
We don't need to dip into /usr/local, since all library/framework headers are already in this repository.

Ensure that there exists at the root of the repository, a folder named .vscode.

.vscode/c_cpp_properties.json

{
    "configurations": [
        {
            "name": "Mac",
            "includePath": [
                "${workspaceFolder}/include",
                "${workspaceFolder}/Source",
                "${workspaceFolder}/JuceLibraryCode",
                "${workspaceFolder}/modules"
            ],
            "defines": [],
            "cStandard": "c11",
            "cppStandard": "c++14",
            "intelliSenseMode": "clang-x64",
            "compilerPath": "/usr/local/Cellar/llvm/8.0.0_1/bin/clang++"
        }
    ],
    "version": 4
}

I've kept this minimal, but documented some other include paths worthy of consideration (e.g. if more parts of the toolchain were to be used, brew were to be used, or the standard XCode clang were to be used).

~/Library/Application Support/Code/User/settings.json

{
    "C_Cpp.updateChannel": "Insiders",
    "C_Cpp.default.intelliSenseMode": "clang-x64",
    "C_Cpp.default.macFrameworkPath": [
        // "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/CoreServices.framework/Frameworks",
        "/System/Library/Frameworks",
        // "/Library/Frameworks"
    ],
    "C_Cpp.default.includePath": [
        // "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1",
        // "/usr/local/include",
        // "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1/include",
        // "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include",
        // "${workspaceFolder}/include"
        // "/usr/include",
        "/usr/local/Cellar/llvm/8.0.0_1/Toolchains/LLVM8.0.0.xctoolchain/usr/include/c++/v1",
        // "/usr/local/Cellar/llvm/8.0.0_1/Toolchains/LLVM8.0.0.xctoolchain/usr/lib/clang/8.0.0/include",
        // "/usr/local/Cellar/llvm/8.0.0_1/Toolchains/LLVM8.0.0.xctoolchain/usr/include",
    ],
    "C_Cpp.default.cStandard": "c11",
    "C_Cpp.default.cppStandard": "c++14",
    "C_Cpp.default.compilerPath": "/usr/local/Cellar/llvm/8.0.0_1/bin/clang++",
    "C_Cpp.clang_format_fallbackStyle": "LLVM",
    "C_Cpp.clang_format_style": "LLVM",
    "C_Cpp.default.browse.limitSymbolsToIncludedHeaders": true,
    "C_Cpp.default.enableConfigurationSquiggles": true,
    "C_Cpp.errorSquiggles": "Enabled",
    "C_Cpp.enhancedColorization": "Enabled"
}

Test matrix

Known working with:

macOS Mojave 10.14.5
Windows 10 x64 1903

Making releases

Follow the steps in Building from source to output a product to the build folder.

Builds are automatically portable.

cd juicysfplugin/Builds/MacOSX
# first check that you have a Release or Debug product in the `build` directory

# follows symlinks, archives Release and Debug folders as tar.xz
./archive-for-distribution.sh

Note: Release and Debug flavors both output targets [VST, VST3, AU] to the same location: ~/Library/Audio/Plug-Ins/$TARGET/juicysfplugin.$EXT.
Whichever flavor you built most recently, wins.

Licenses

Overall, juicysfplugin is GPLv3.

See licenses for all libraries and frameworks.