A powerful SF2/DLS/MIDI JavaScript library. It works with any modern JS environment that supports WebAssembly.

TIP: Looking for an easy-to-use WebAudioAPI browser wrapper? Try spessasynth_lib!

npm install --save spessasynth_core

Note: This is the new heart of the SpessaSynth library, after the repository has been split.

Project index

• spessasynth_core (you are here) - SF2/DLS/MIDI library
• spessasynth_lib - spessasynth_core wrapper optimized for browsers and WebAudioAPI
• SpessaSynth - online/local web player/editor application

• Modular design: Easy integration into other projects (load what you need)
• Detailed documentation: With examples!
• Flexible: It's not just a MIDI player!
• Easy to Use: Basic setup is just two lines of code!
• No dependencies: Batteries included!

• Suitable for both real-time and offline synthesis
• Excellent SoundFont support:
  • Full Generator Support
  • Full Modulator Support: First (to my knowledge) JavaScript SoundFont synth with that feature!
  • GeneralUserGS Compatible: See more here!
  • SoundFont3 Support: Play compressed SoundFonts!
  • Experimental SF2Pack Support: Play soundfonts compressed with BASSMIDI! (Note: only works with vorbis compression)
  • Can load very large SoundFonts: up to 4GB! Note: Only Firefox handles this well; Chromium has a hard-coded memory limit
• Great DLS Support:
  • DLS Level 1 Support
  • DLS Level 2 Support
  • Mobile DLS Support
  • Correct articulator support: Converts articulators to both modulators and generators!
  • Tested and working with gm.dls!
  • Correct volume: Properly translated to SoundFont volume!
  • A-Law encoding support
  • Both unsigned 8-bit and signed 16-bit sample support (24-bit theoretically supported as well!)
  • Detects special articulator combinations: Such as vibratoLfoToPitch
• Soundfont manager: Stack multiple soundfonts!
• Unlimited channel count: Your CPU is the limit!
• Excellent MIDI Standards Support:
  • MIDI Controller Support: Default supported controllers here
  • Portamento Support: Glide the notes!
  • Sound Controllers: Real-time filter and envelope control!
  • MIDI Tuning Standard Support: more info here
  • Full RPN and limited NRPN support
  • AWE32 NRPN Compatibility Layer
  • Supports some Roland GS and Yamaha XG system exclusives

• Supports MIDI formats 0, 1, and 2: note: format 2 support is experimental as it's very, very rare.
• Multi-Port MIDI support: More than 16 channels!
• Smart preloading: Only preloads the samples used in the MIDI file for smooth playback (down to key and velocity!)
• Lyrics support: Add karaoke to your program!
• Raw lyrics available: Decode in any encoding! (Kanji? No problem!)
• Runs in Audio Thread as well: Never blocks the main thread
• Loop points support: Ensures seamless loops

• Smart name detection: Handles incorrectly formatted and non-standard track names
• Raw name available: Decode in any encoding! (Kanji? No problem!)
• Port detection during load time: Manage ports and channels easily!
• Used channels on track: Quickly determine which channels are used
• Key range detection: Detect the key range of the MIDI
• Easy MIDI editing: Use helper functions to modify the song to your needs!
• Loop detection: Automatically detects loops in MIDIs (e.g., from Touhou Project)
• First note detection: Skip unnecessary silence at the start by jumping to the first note!
• Lyrics support: Both regular MIDI and .kar files!
• Write MIDI files from scratch
• Easy saving: Save with just one function!

• Level 4 compliance: Reads and writes everything!
• Compression and trimming support: Reduce a MIDI file with a 1GB soundfont to as small as 5MB!
• DLS Version support: The original legacy format with bank offset detection!
• Automatic bank shifting and validation: Every soundfont just works!
• Metadata support: Add title, artist, album name and cover and more! And of course, read them too! (In any encoding!)
• Compatible with Falcosoft Midi Player 6!
• Easy saving: As simple as saving a MIDI file!

• Easy info access: Just an object of strings!
• Smart trimming: Trim the SoundFont to only include samples used in the MIDI (down to key and velocity!)
• sf3 conversion: Compress SoundFont2 files to SoundFont3 with variable quality!
• Easy saving: Also just one function!

• Same features as SoundFont2 but with now with Ogg Vorbis compression!
• Variable compression quality: You choose between file size and quality!
• Compression preserving: Avoid decompressing and recompressing uncompressed samples for minimal quality loss!

• Read DLS (DownLoadable Sounds) files as SF2 files!
• Works like a normal soundfont: Saving it as sf2 is still just one function!
• Converts articulators to both modulators and generators!
• Works with both unsigned 8-bit samples and signed 16-bit samples!
• A-Law encoding support
• Covers special generator cases: such as modLfoToPitch!
• Correct volume: looking at you, Viena and gm.sf2!
• Support built right into the synthesizer!
• Convert SF2 to DLS: with limitations

• Save the MIDI file as WAV audio!
• Metadata support: Embed metadata such as title, artist, album and more!
• Cue points: Write MIDI loop points as cue points!
• Loop multiple times: Render two (or more) loops into the file for seamless transitions!
• That's right, saving as WAV is also just one function!

• Synth's performance may be questionable sometimes
• SF2 to DLS Conversion limits

• Improve the performance of the engine
• Potentially port the system to Emscripten

• FluidSynth - for the source code that helped implement functionality and fixes
• Polyphone - for the soundfont 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
• 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 :)

If you like this project, consider giving it a star. It really helps out!

import * as fs from "node:fs";
import { MIDI, SpessaSynthProcessor, SpessaSynthSequencer, audioToWav, loadSoundFont } from "spessasynth_core";

// process arguments
const args = process.argv.slice(2);
if (args.length !== 3)
{
    console.log("Usage: node index.js <soundfont path> <midi path> <wav output path>");
    process.exit();
}
const sf = fs.readFileSync(args[0]);
const mid = fs.readFileSync(args[1]);
const midi = new MIDI(mid);
const sampleRate = 44100;
const sampleCount = 44100 * (midi.duration + 2);
const synth = new SpessaSynthProcessor(sampleRate, {
    enableEventSystem: false,
    effectsEnabled: false
});
synth.soundfontManager.reloadManager(loadSoundFont(sf));
await synth.processorInitialized;
const seq = new SpessaSynthSequencer(synth);
seq.loadNewSongList([midi]);
seq.loop = false;
const outLeft = new Float32Array(sampleCount);
const outRight = new Float32Array(sampleCount);
const start = performance.now();
let filledSamples = 0;
// note: buffer size is recommended to be very small, as this is the interval between modulator updates and LFO updates
const bufSize = 128;
let i = 0;
while (filledSamples + bufSize < sampleCount)
{
    const bufLeft = new Float32Array(bufSize);
    const bufRight = new Float32Array(bufSize);
    // process sequencer
    seq.processTick();
    const arr = [bufLeft, bufRight];
    // render
    synth.renderAudio(arr, arr, arr);
    // write out
    outLeft.set(bufLeft, filledSamples);
    outRight.set(bufRight, filledSamples);
    filledSamples += bufSize;
    i++;
    // log progress
    if (i % 100 === 0)
    {
        console.log("Rendered", seq.currentTime, "/", midi.duration);
    }
}
console.log("Rendered in", Math.floor(performance.now() - start), "ms");
const wave = audioToWav({
    leftChannel: outLeft,
    rightChannel: outRight,
    sampleRate: sampleRate
});
fs.writeFileSync(args[2], new Buffer(wave));
process.exit();

Copyright © 2025 Spessasus Licensed under the Apache-2.0 License.

This project is in no way endorsed or otherwise affiliated with the MIDI Manufacturers Association, Creative Technology Ltd. or E-mu Systems, Inc., or any other organization mentioned. SoundFont® is a registered trademark of Creative Technology Ltd. All other trademarks are the property of their respective owners.