A powerful SF2/DLS/MIDI JavaScript library for the browsers, based on spessasynth_core. This is a WebAudioAPI wrapper for the spessasynth_core library.
v4.0.0 TypeScript Update is here! The NPM package now contains type declarations for easier developing! Read about breaking changes here
It allows you to:
- Play MIDI files using SF2/SF3/DLS files!
- Read and write MIDI files!
- Write SF2/SF3 files!
- Convert DLS to SF2! (and back!)
- and more!
TIP:
Looking for a bare JS version that works without WebAudioAPI? Try spessasynth_core!
SpessaSynth Project index
- spessasynth_core - SF2/DLS/MIDI library
- spessasynth_lib (you are here) - spessasynth_core wrapper optimized for browsers and WebAudioAPI
- SpessaSynth - online/local MIDI player/editor application
- SpessaFont - online SF2/DLS editor
- Fully typed: Faster development and IDE auto-completion!
- Modular design: Easy integration into other projects (load what you need)
- Detailed documentation: With examples!
- Easy to Use: Basic setup is just two lines of code!
- No external dependencies: Just spessasynth_core!
- Reverb and chorus support: customizable and can be used standalone!
- Export audio files using OfflineAudioContext!
- AudioWorklet synthesizer:
- Runs in a separate thread for maximum performance!
- Does not stop playing even when the main thread is frozen!
- Supported by all modern browsers!
- Web Worker synthesizer:
- Synthesize directly in the Web Worker!
- Direct audio engine access!
- Export audio automatically in the worker!
- Avoids Chromium Audio Bugs!
- High-performance mode: Play Rush E! note: may kill your browser ;)
- FluidSynth - for the source code that helped implement functionality and fixes
- Polyphone - for the sound bank testing and editing tool
- Meltysynth - for the initial low-pass filter implementation
- RecordingBlogs - for detailed explanations on MIDI messages
- stbvorbis.js - for the Vorbis decoder
- fflate - for the MIT DEFLATE implementation
- tsup - for the TypeScript bundler
- foo_midi - for useful resources on XMF file format
- Falcosoft - for help with the RMIDI format
- Christian Collins - for various bug reports regarding the synthesizer
- And You! - for checking out this project. I hope you like it :)
import { WorkletSynthesizer } from "spessasynth_lib"
// SF2, SF3, SFOGG and DLS files are all supported!
const sfont = await (await fetch("soundfont.sf3")).arrayBuffer();
const ctx = new AudioContext();
// make sure you copied the worklet processor!
await ctx.audioWorklet.addModule("./spessasynth_processor.min.js");
const synth = new WorkletSynthesizer(ctx);
await synth.soundBankManager.addSoundBank(sfont, "main");
await synth.isReady;
document.getElementById("button").onclick = async () =>
{
await ctx.resume();
synth.programChange(0, 48); // strings ensemble
synth.noteOn(0, 52, 127);
}Copyright © 2025 Spessasus Licensed under the Apache-2.0 License.
SoundFont® is a registered trademark of Creative Technology Ltd.