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

Suitable for both real-time and offline synthesis.
Support for standard MIDI files with additional functionalities like dynamic tempo change.
No dependencies other than .NET Standard 2.1.

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

Examples

MIDI file player for various audio drivers

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);
}

Handling MIDI file sequencer

To change the playback speed:

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

// Read the MIDI file.
var midiFile = new MidiFile(@"C:\Windows\Media\flourish.mid");
var sequencer = new MidiFileSequencer(synthesizer);

// Play the MIDI file.
sequencer.Play(midiFile, false);

// Change the playback speed.
sequencer.Speed = 1.5F;

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

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

To mute a certain track:

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

// Read the MIDI file.
var midiFile = new MidiFile(@"C:\Windows\Media\flourish.mid");
var sequencer = new MidiFileSequencer(synthesizer);

// Discard MIDI messages if its channel is the percussion channel.
sequencer.OnSendMessage = (synthesizer, channel, command, data1, data2) =>
{
    if (channel == 9)
    {
        return;
    }

    synthesizer.ProcessMidiMessage(channel, command, data1, data2);
};

// Play the MIDI file.
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);

To change the instruments used in the MIDI file:

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

// Read the MIDI file.
var midiFile = new MidiFile(@"C:\Windows\Media\flourish.mid");
var sequencer = new MidiFileSequencer(synthesizer);

// Turn all the instruments into electric guitars.
sequencer.OnSendMessage = (synthesizer, channel, command, data1, data2) =>
{
    if (command == 0xC0)
    {
        data1 = 30;
    }

    synthesizer.ProcessMidiMessage(channel, command, data1, data2);
};

// Play the MIDI file.
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);

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

mobilewish/meltysynth