orgel.js

// Reference: https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API/Simple_synth

"use strict"

export { setup, playTones, stop, Tone };

class Tone {
  constructor(octave, note, startAt, duration) {
    this.octave = octave;
    this.note = note;
    this.startAt = startAt;
    this.duration = duration;
  }
}

let contexts = [];
let noteFrequencies = null;

function createNoteTable() {
  let noteFreq = [];
  for (let i=0; i< 9; i++) {
    noteFreq[i] = [];
  }

  noteFreq[0]["A"] = 27.500000000000000;
  noteFreq[0]["A#"] = 29.135235094880619;
  noteFreq[0]["B"] = 30.867706328507756;

  noteFreq[1]["C"] = 32.703195662574829;
  noteFreq[1]["C#"] = 34.647828872109012;
  noteFreq[1]["D"] = 36.708095989675945;
  noteFreq[1]["D#"] = 38.890872965260113;
  noteFreq[1]["E"] = 41.203444614108741;
  noteFreq[1]["F"] = 43.653528929125485;
  noteFreq[1]["F#"] = 46.249302838954299;
  noteFreq[1]["G"] = 48.999429497718661;
  noteFreq[1]["G#"] = 51.913087197493142;
  noteFreq[1]["A"] = 55.000000000000000;
  noteFreq[1]["A#"] = 58.270470189761239;
  noteFreq[1]["B"] = 61.735412657015513;

  noteFreq[2]["C"] = 65.406391325149658;
  noteFreq[2]["C#"] = 69.295657744218024;
  noteFreq[2]["D"] = 73.416191979351890;
  noteFreq[2]["D#"] = 77.781745930520227;
  noteFreq[2]["E"] = 82.406889228217482;
  noteFreq[2]["F"] = 87.307057858250971;
  noteFreq[2]["F#"] = 92.498605677908599;
  noteFreq[2]["G"] = 97.998858995437323;
  noteFreq[2]["G#"] = 103.826174394986284;
  noteFreq[2]["A"] = 110.000000000000000;
  noteFreq[2]["A#"] = 116.540940379522479;
  noteFreq[2]["B"] = 123.470825314031027;

  noteFreq[3]["C"] = 130.812782650299317;
  noteFreq[3]["C#"] = 138.591315488436048;
  noteFreq[3]["D"] = 146.832383958703780;
  noteFreq[3]["D#"] = 155.563491861040455;
  noteFreq[3]["E"] = 164.813778456434964;
  noteFreq[3]["F"] = 174.614115716501942;
  noteFreq[3]["F#"] = 184.997211355817199;
  noteFreq[3]["G"] = 195.997717990874647;
  noteFreq[3]["G#"] = 207.652348789972569;
  noteFreq[3]["A"] = 220.000000000000000;
  noteFreq[3]["A#"] = 233.081880759044958;
  noteFreq[3]["B"] = 246.941650628062055;

  noteFreq[4]["C"] = 261.625565300598634;
  noteFreq[4]["C#"] = 277.182630976872096;
  noteFreq[4]["D"] = 293.664767917407560;
  noteFreq[4]["D#"] = 311.126983722080910;
  noteFreq[4]["E"] = 329.627556912869929;
  noteFreq[4]["F"] = 349.228231433003884;
  noteFreq[4]["F#"] = 369.994422711634398;
  noteFreq[4]["G"] = 391.995435981749294;
  noteFreq[4]["G#"] = 415.304697579945138;
  noteFreq[4]["A"] = 440.000000000000000;
  noteFreq[4]["A#"] = 466.163761518089916;
  noteFreq[4]["B"] = 493.883301256124111;

  noteFreq[5]["C"] = 523.251130601197269;
  noteFreq[5]["C#"] = 554.365261953744192;
  noteFreq[5]["D"] = 587.329535834815120;
  noteFreq[5]["D#"] = 622.253967444161821;
  noteFreq[5]["E"] = 659.255113825739859;
  noteFreq[5]["F"] = 698.456462866007768;
  noteFreq[5]["F#"] = 739.988845423268797;
  noteFreq[5]["G"] = 783.990871963498588;
  noteFreq[5]["G#"] = 830.609395159890277;
  noteFreq[5]["A"] = 880.000000000000000;
  noteFreq[5]["A#"] = 932.327523036179832;
  noteFreq[5]["B"] = 987.766602512248223;

  noteFreq[6]["C"] = 1046.502261202394538;
  noteFreq[6]["C#"] = 1108.730523907488384;
  noteFreq[6]["D"] = 1174.659071669630241;
  noteFreq[6]["D#"] = 1244.507934888323642;
  noteFreq[6]["E"] = 1318.510227651479718;
  noteFreq[6]["F"] = 1396.912925732015537;
  noteFreq[6]["F#"] = 1479.977690846537595;
  noteFreq[6]["G"] = 1567.981743926997176;
  noteFreq[6]["G#"] = 1661.218790319780554;
  noteFreq[6]["A"] = 1760.000000000000000;
  noteFreq[6]["A#"] = 1864.655046072359665;
  noteFreq[6]["B"] = 1975.533205024496447;

  noteFreq[7]["C"] = 2093.004522404789077;
  noteFreq[7]["C#"] = 2217.461047814976769;
  noteFreq[7]["D"] = 2349.318143339260482;
  noteFreq[7]["D#"] = 2489.015869776647285;
  noteFreq[7]["E"] = 2637.020455302959437;
  noteFreq[7]["F"] = 2793.825851464031075;
  noteFreq[7]["F#"] = 2959.955381693075191;
  noteFreq[7]["G"] = 3135.963487853994352;
  noteFreq[7]["G#"] = 3322.437580639561108;
  noteFreq[7]["A"] = 3520.000000000000000;
  noteFreq[7]["A#"] = 3729.310092144719331;
  noteFreq[7]["B"] = 3951.066410048992894;

  noteFreq[8]["C"] = 4186.009044809578154;
  return noteFreq;
}

function setup() {
  noteFrequencies = createNoteTable();
}

function playTones(tones) {
  let audioContext = new (window.AudioContext || window.webkitAudioContext)();
  contexts.push(audioContext);
  tones.forEach(tone => {
    let osc = audioContext.createOscillator();
    let gainNode = audioContext.createGain();
    gainNode.connect(audioContext.destination);
    gainNode.gain.value = 1;

    osc.connect(gainNode);
    osc.type = "sine";  // sine, square, triangle, and sawtooth
    osc.frequency.value = noteFrequencies[tone.octave][tone.note];

    const startTime = audioContext.currentTime + tone.startAt / 8;
    const endTime = audioContext.currentTime + tone.startAt / 8 + tone.duration / 8;
    osc.start(startTime);
    osc.stop(endTime);
    gainNode.gain.linearRampToValueAtTime(1, endTime - 0.2);
    gainNode.gain.linearRampToValueAtTime(0, endTime);
  });
}


function stop() {
  contexts.forEach(context => context.close())
  contexts = [];
}