polySynth.js

This module is a wrapper to play around with the web audio API. It provides a polyphonicSynth class.

Polyphonic Synth

Module can be imported with

import { polyphonicSynth } from "./PolySynth.js";

It can be used by creating a new instance of the synth:

let synth = new polyphonicSynth(audioCtx,waveForm,output,envelope);

waveForm can be created with audioCtx.createPeriodicWave(), output is typically a master gain or a dynamic compressor and envelope is an object, which controls an ADSR envelope. It is defined as follows:

let envelope = {
  attackTime:[seconds],
  attackLevel:[0-1 range],
  decayTime:[seconds],
  decayLevel:[0-1 range],
  releaseTime:[seconds],
  linear:[boolean]
};

The synth can be used to play notes with:

synth.noteOn(midi_note)

and

synth.noteOff(midi_note)

Solfeggio helper

A solfeggio-helper module is also provided, so one doesn't have to handle MIDI but human notation:

import { Music } from "./Music.js";

This solfeggio helper provides various functions :

Music.noteNameToMidi(human_note,absolute) is used to performed conversion from note name (eg. C#) to MIDI (eg. 1). The facultative absolute flag, true by default, transposes the output note to medium registry (if set to false, C# would output 61 instead of 1).

The base octave toggled by this flag can be set with Music.setHeight(octaves). Default value for octaves argument is 5.

Scales can be generated with Music.generateScale(tonic,mode), where tonic can be a MIDI value or a note. Mode is an array consisting of a series of intervals, in semitones (eg. for major/ionian mode : [2,2,1,2,2,2,1]). Note names in their usual order (eg. a C major Scale) is already built-in in Music.SOLMISATION.

The modules also comes with built-in classical modes: Major and minor modes can be accessed through Music.MAJOR & Music.MINOR. Jazz/Medieval modes can be found inside the Music.MODES object. For example Music.MODES.AEOLIAN is equivalent to Music.MINOR. Modes names in their usual order is stored in the Music.MODE_NAMES array.

Alternatively, any mode can be created by the Music.makeMode(reference_note,reference_mode) method: Music.makeMode("A",Music.MAJOR) would generate the equivalent of Music.MODES.AEOLIAN (or Music.MINOR). One could generate a minor pentatonic by doing Music.makeMode(2,[2,2,3,2]).

Music.makeChord(chord_object) is used to generate chords. To chord_object is defined by four parameters: its tonic, its mode, its degree and position.

let chord = {
  tonic:"C#",
  degree:2,
  mode:"D",
  position:1
};

The tonic parameter is pretty self-explanatory. It can be either a note or a MIDI number. The mode parameter can be an array, as seen above, or a shifting note to generate a mode (in the example, generated mode will be dorian). The degree is the desired position of the chord within the defined scale, as usually written in roman numeration. Here we have a IInd degree of the C# scale in dorian mode, hence a D# minor. The position is the inversion of the chord. 0 means no inversion, 1 would mean the third of the chord is used as bass, and so on.

Example

It is now possible to build a small sequencer, for example we create here a classic jazz II-V-I progression in Bb phrygian:

(async () => {
  let durations = [400,400,600];
  let sequence = [2,5,1];
  for (let i in sequence) {
    let chord = {
      tonic:"Bb",
      degree:sequence[i],
      mode:"E",
      position:1
    };
    chord = Music.makeChord(chord);
    let voices = chord.map(e => synth.noteOn(e));
    await ((t) => {
      return new Promise((resolve,reject) => {
        setTimeout(() => { resolve(); },t)
      })
    })(durations[i]);
    voices.map(e => synth.noteOff(e));
  }
})()