MeltySynth

MeltySynth is a SoundFont synthesizer written in C#. The purpose of this project is to provide a MIDI music playback functionality for any .NET applications without complicated dependencies. The codebase is lightweight and can be applied to any audio drivers which support streaming audio, such as SFML.Net, Silk.NET, OpenTK, and NAudio.

The entire code is heavily inspired by the following projects:

• C# Synth by Alex Veltsistas
• TinySoundFont by Bernhard Schelling

An example code to synthesize a simple chord:

// Create the synthesizer.
var sampleRate = 44100;
var synthesizer = new Synthesizer("TimGM6mb.sf2", sampleRate);

// Play some notes (middle C, E, G).
synthesizer.NoteOn(0, 60, 100);
synthesizer.NoteOn(0, 64, 100);
synthesizer.NoteOn(0, 67, 100);

// The output buffer (3 seconds).
var left = new float[3 * sampleRate];
var right = new float[3 * sampleRate];

// Render the waveform.
synthesizer.Render(left, right);

Another example code to synthesize a MIDI file:

// Create the synthesizer.
var sampleRate = 44100;
var synthesizer = new Synthesizer("TimGM6mb.sf2", sampleRate);

// Read the MIDI file.
var midiFile = new MidiFile("flourish.mid");
var sequencer = new MidiFileSequencer(synthesizer);
sequencer.Play(midiFile, false);

// The output buffer.
var left = new float[(int)(sampleRate * midiFile.Length.TotalSeconds)];
var right = new float[(int)(sampleRate * midiFile.Length.TotalSeconds)];

// Render the waveform.
sequencer.Render(left, right);

Features

• No dependencies other than .NET Standard 2.1.
• No memory allocation in the rendering process.
• No unsafe code.

Installation

The NuGet package is available:

Install-Package MeltySynth

All the classes are in the MeltySynth namespace:

using MeltySynth;

If you don't like DLLs, copy all the .cs files to your project.

Playing sound

MeltySynth can only generate PCM waveforms; MeltySynth itself does not have the ability to play sound from speakers. To make the sound audible, export the generated waveform as an audio file (e.g., WAV file) or pass it to some audio driver (e.g., NAudio). If you are not very familiar with how to handle PCM audio, NAudio's tutorials should be helpful.

Note that MeltySynth does not provide thread safety. If you want to send notes and render the waveform in separate threads, you must ensure that the related methods will not be called simultaneously.

Demo

A demo song generated with Arachno SoundFont

https://www.youtube.com/watch?v=xNgsIJKxPkI

A Doom port written in C# with MIDI music playback

https://www.youtube.com/watch?v=_j1izHgIT4U

A virtual keyboard made with Raylib-CsLo

https://www.youtube.com/watch?v=a8vuIq4JKhs

Use MeltySynth as a MIDI device (NAudio + loopMIDI)

https://www.youtube.com/watch?v=BiFxvzs0jUI

Use MeltySynth as a VST plugin (VST.NET)

https://www.youtube.com/watch?v=IUKIEWvw6Ik

Examples

MIDI file player for various audio drivers

• MIDI file player for SFML.Net
• MIDI file player for Silk.NET (OpenAL)
• MIDI file player for Silk.NET (SDL)
• MIDI file player for OpenTK
• MIDI file player for SDL2#
• MIDI file player for Sokol_csharp
• MIDI file player for MonoGame
• MIDI file player for FNA.NET
• MIDI file player for Raylib-cs
• MIDI file player for Raylib-CsLo
• MIDI file player for DotFeather
• MIDI file player for NAudio
• MIDI file player for CSCore
• MIDI file player for TinyAudio
• MIDI file player for DrippyAL

Handling SoundFont

To enumerate samples in the SoundFont:

var soundFont = new SoundFont("TimGM6mb.sf2");

foreach (var sample in soundFont.SampleHeaders)
{
    Console.WriteLine(sample.Name);
}

To enumerate instruments in the SoundFont:

var soundFont = new SoundFont("TimGM6mb.sf2");

foreach (var instrument in soundFont.Instruments)
{
    Console.WriteLine(instrument.Name);
}

To enumerate presets in the SoundFont:

var soundFont = new SoundFont("TimGM6mb.sf2");

foreach (var preset in soundFont.Presets)
{
    var bankNumber = preset.BankNumber.ToString("000");
    var patchNumber = preset.PatchNumber.ToString("000");

    Console.WriteLine($"{bankNumber}:{patchNumber} {preset.Name}");
}

Handling synthesizer

To change the instrument to play, send a program change command (0xC0) to the synthesizer:

// Create the synthesizer.
var sampleRate = 44100;
var synthesizer = new Synthesizer("TimGM6mb.sf2", sampleRate);

// Change the instrument to electric guitar (#30).
synthesizer.ProcessMidiMessage(0, 0xC0, 30, 0);

// Play some notes (middle C, E, G).
synthesizer.NoteOn(0, 60, 100);
synthesizer.NoteOn(0, 64, 100);
synthesizer.NoteOn(0, 67, 100);

// The output buffer (3 seconds).
var left = new float[3 * sampleRate];
var right = new float[3 * sampleRate];

// Render the waveform.
synthesizer.Render(left, right);

To play a melody, render the sound as a sequence of short blocks:

// Create the synthesizer.
var sampleRate = 44100;
var synthesizer = new Synthesizer("TimGM6mb.sf2", sampleRate);

// The length of a block is 0.1 sec.
var blockSize = sampleRate / 10;

// The entire output is 3 sec.
var blockCount = 30;

// Define the melody.
// A single row indicates the start timing, end timing, and pitch.
var data = new int[][]
{
    new int[] {  5, 10, 60 },
    new int[] { 10, 15, 64 },
    new int[] { 15, 25, 67 }
};

// The output buffer.
var left = new float[blockSize * blockCount];
var right = new float[blockSize * blockCount];

for (var t = 0; t < blockCount; t++)
{
    // Process the melody.
    foreach (var row in data)
    {
        if (t == row[0]) synthesizer.NoteOn(0, row[2], 100);
        if (t == row[1]) synthesizer.NoteOff(0, row[2]);
    }

    // Render the block.
    var blockLeft = left.AsSpan(blockSize * t, blockSize);
    var blockRight = right.AsSpan(blockSize * t, blockSize);
    synthesizer.Render(blockLeft, blockRight);
}

Todo

• Wave synthesis
  • SoundFont reader
  • Waveform generator
  • Envelope generator
  • Low-pass filter
  • Vibrato LFO
  • Modulation LFO
• MIDI message processing
  • Note on/off
  • Bank selection
  • Modulation
  • Volume control
  • Pan
  • Expression
  • Hold pedal
  • Program change
  • Pitch bend
  • Tuning
• Effects
  • Reverb
  • Chorus
• Other things
  • Standard MIDI file support
  • Loop extension support
  • Performace optimization

License

MeltySynth is available under the MIT license.

References

• SoundFont® Technical Specification
  http://www.synthfont.com/SFSPEC21.PDF

• Polyphone Soundfont Editor
  Some of the test cases were generated with Polyphone.
  https://www.polyphone-soundfonts.com/

• Freeverb by Jezar at Dreampoint
  The implementation of the reverb effect is based on Freeverb.
  https://music.columbia.edu/pipermail/music-dsp/2001-October/045433.html