Creating MIDI Files

Creating MIDI files

SpessaSynth allows you to create MIDI files from scratch via MIDIBuilder

Importing

// normal install
import { MIDIBuilder } from "./spessasynth_lib/midi_parser/midi_builder.js";
// npm package
import { MIDIBuilder } from "spessasynth_lib";

Tip

Using the npm package? Make sure you've read this

Initialization

const mid = new MIDIBuilder(name, timeDivision = 480, initialTempo = 120);

• name - string - the MIDI's name. The first event of the first track will be the track name with this.
• timeDivision - number, optional - the MIDI's time division. Defaults to 480.
• initialTempo - number, optional - the MIDI's initial tempo in beats per minute. Defaults to 120 BPM.

The file is initialized with one track.

This class inherits from MIDI which means it can simply be passed to writeMIDIFile or Sequencer.

Methods

flush

Updates the internal values of the file, making it ready for playback.

Caution

You MUST ALWAYS run this function after you finish creating the file!

mid.flush();

addNewTrack

Adds a new MIDI track. Changes the format to 1.

mid.addNewTrack(name, port = 0);

• name - string - The track's name. The first event will be track name with this.
• port - number, optional - the MIDI port to use. Leave it at 0, unless you know what you're doing.

addEvent

Adds a new MIDI event.

mid.addEvent(ticks, track, event, eventData);

• ticks - number - the MIDI tick time of the event.
• track - number - the track to use.
• event - number - the MIDI status byte of the message.
• eventData - Uint8Array or number[] - the message's binary data.

Caution

For meta messages, the event is the SECOND status byte, not the 0xFF! For system exclusives, the status byte is F0 and it must be excluded from eventData!

addSetTempo

Adds a new "set tempo" message.

mid.addSetTempo(ticks, tempo);

• ticks - number - the MIDI tick time of the event.
• tempo - number - the new tempo in beats per minute.

addNoteOn

Adds a new "note on" message.

mid.addNoteOn(ticks, track, channel, midiNote, velocity);

• ticks - number - the MIDI tick time of the event.
• track - number - the track to use.
• channel - number - the MIDI channel to use. Ranges from 0 to 15.
• midiNote - number - the MIDI key number to press. Ranges from 0 to 127.
• velocity - number - the velocity (strength) of the keypress. Ranges from 0 to 127. A value of 0 is equal to "note off" message.

addNoteOff

Adds a new "note off" message.

mid.addNoteOff(ticks, track, channel, midiNote);

• ticks - number - the MIDI tick time of the event.
• track - number - the track to use.
• channel - number - the MIDI channel to use. Ranges from 0 to 15.
• midiNote - number - the MIDI key number to release. Ranges from 0 to 127.

addControllerChange

Adds a new "controller change" message.

mid.addControllerChange(ticks, track, channel, controllerNumber, controllerValue);

• ticks - number - the MIDI tick time of the event.
• track - number - the track to use.
• channel - number - the MIDI channel to use. Ranges from 0 to 15.
• controllerNumber - number - the MIDI Controller Number to change.
• controllerValue - number - the new value of the controller. 0 to 127.

addPitchWheel

Adds a new "pitch wheel" message.

mid.addPitchWheel(ticks, track, channel, MSB, LSB);

• ticks - number - the MIDI tick time of the event.
• track - number - the track to use.
• channel - number - the MIDI channel to use. Ranges from 0 to 15.
• MSB and LSB - both number - 7-bit numbers that form a 14-bit pitch bend value.

Tip

I highly recommend this article for more info.

Example usage

The below code produces a file that plays C Major scale.

// Create a new MIDI file
const mid = new MIDIBuilder("C Major Scale", 480, 240);

// Add the C Major scale notes
mid.addNoteOn(0, 0, 0, 60, 127);
mid.addNoteOff(1250, 0, 0, 60);
mid.addNoteOn(1250, 0, 0, 62, 127);
mid.addNoteOff(2500, 0, 0, 62);
mid.addNoteOn(2500, 0, 0, 64, 127);
mid.addNoteOff(3750, 0, 0, 64);
mid.addNoteOn(3750, 0, 0, 65, 127);
mid.addNoteOff(5000, 0, 0, 65);
mid.addNoteOn(5000, 0, 0, 67, 127);
mid.addNoteOff(6250, 0, 0, 67);
mid.addNoteOn(6250, 0, 0, 69, 127);
mid.addNoteOff(7500, 0, 0, 69);
mid.addNoteOn(7500, 0, 0, 71, 127);
mid.addNoteOff(8750, 0, 0, 71);
mid.addNoteOn(8750, 0, 0, 72, 127);
mid.addNoteOff(10000, 0, 0, 72);

// Finalize the MIDI file
mid.flush();

// Write the MIDI file to a blob and save it
const b = writeMIDIFile(mid);
const blob = new Blob([b.buffer], { type: "audio/mid" });
const url = URL.createObjectURL(blob);
const a = document.createElement("a");
a.href = url;
a.download = "C_major_scale.mid";
a.click();