function getFrequency(n) {
  return Math.round(440 * Math.pow(2, (piano.length - piano.indexOf(n) - 1 + 3 - 36) / 12));
}

var synthTypes = ['sine', 'square', 'sawtooth', 'triangle'];

var poly = 64;
var oscillators = [{},{},{},{}];
var synthTime = 0;

function initSynth(context, id) {
  for (var i = 0; i < piano.length; i++) {
    var n = piano[i];
    oscillators[id][n] = context.createOscillator();
    var o = oscillators[id][n];
    o.type = synthTypes[id];
    o.frequency.value = getFrequency(n);

    var gain = context.createGain();
    gain.gain.value = 0;
    o.connect(gain);
    gain.connect(audioSystem.gainNodes[id + 13]);

    o.gain = gain;
    o.inUse = false;
    o.inUseTime = 0;

    o.start ? o.start(0) : o.noteOn(0);
  }
}

function playSynthNote(context, id, note, time) {
  synthTime++;
  var oscillator = oscillators[id][note];
  if (oscillator) {
    (function (synthTime) {
      oscillator.inUseTime = synthTime;
      oscillator.inUse = true;
      oscillator.gain.gain.value = 0.1 * audioSystem.masterVolume;
      window.setTimeout(function () {
        if (oscillator.inUseTime == synthTime) {
          oscillator.gain.gain.value = 0;
          oscillator.inUse = false;
        }
      }, time);
    })(synthTime);
  }
}