Microtonal JS

microtonal.js

// https://pages.mtu.edu/~suits/notefreqs.html
// https://pages.mtu.edu/~suits/NoteFreqCalcs.html

// create web audio api context
var audioCtx = new(window.AudioContext || window.webkitAudioContext)();
// microtonal division
var microtonalDiv = 24;
var c4 = 261.6256;


function oscillateNote(frequency, duration) {
  // create Oscillator node
  var oscillator = audioCtx.createOscillator();

  oscillator.type = 'wave';
  oscillator.frequency.value = frequency; // value in hertz
  oscillator.connect(audioCtx.destination);
  oscillator.start();

  setTimeout(
    function() {
      oscillator.stop();
    }, duration);
}

function noteToFreq(note, pitch, octave){ 
  // note = note.toLowerCase().charCodeAt(0) - 97;
  octave -= 4;
  
  // determine tone
  freq = note.toLowerCase()
  
  // determine note
  switch(note) {
    case 'c':
      freq = 0 + (octave * microtonalDiv);
      break;
    case 'd':
      freq = 4 + (octave * microtonalDiv);
      break;
    case 'e':
      freq = 8 + (octave * microtonalDiv);
      break;
    case 'f':
      freq = 10 + (octave * microtonalDiv);
      break;
    case 'g':
      freq = 14 + (octave * microtonalDiv);
      break;
    case 'a':
      freq = 18 + (octave * microtonalDiv);
      break;
    case 'b':
      freq = 22 + (octave * microtonalDiv);
      break;
    default:
      console.error('NO TONE', freq)
      return;
  }
  
  // determine microtonal note
  // based on: https://github.com/0xfe/vexflow/wiki/Microtonal-Support
  switch(pitch) {
    case 'bb':
      freq -= 4;
      break;
    case 'db':
      freq -= 3;
      break;
    case 'b':
      freq -= 2;
      break;
    case 'bs':
      freq -= 1;
      break;
    case 'n':
      break; 
    case '+':
      freq += 1;
      break;
    case '#':
      freq += 2;
      break;
    case '++':
      freq += 3;
      break;
    case '##':
      freq += 4;
      break;
    default:
      console.error('NO PITCH', freq)
      return;
  }
    
  return c4 * Math.pow(Math.pow(2, 1/microtonalDiv), freq);
}

function playNote(note, mnemonic, octave, duration){
  oscillateNote(noteToFreq(note, mnemonic, octave), duration);
  console.log('playing: ' + noteToFreq(note, mnemonic, octave) + ' as ' + note + mnemonic + octave);
}