Mario Kart wavepot song

mario-kart.js

var pitches = {
  'B2':  123,
  'C3':  131,
  'C#3': 139,
  'D3':  147,
  'D#3': 156,
  'E3':  165,
  'F3':  175,
  'F#3': 185,
  'G3':  196,
  'G#3': 208,
  'A3':  220,
  'A#3': 233,
  'B3':  247,
  'C4':  262,
  'C#4': 278,
  'D4':  294,
  'D#4': 311,
  'E4':  330,
  'F4':  349,
  'F#4': 370,
  'G4':  392,
  'G#4': 415,
  'A4':  440,
  'A#4': 466,
  'B4':  494,
  'C5':  523
}

function Square(gain) {
  this.gain = gain;
  this.notes = {};
  this.length = 0;
}

Square.prototype.addNote = function(pitchName, start, length) {
  var stop = start + length;
  for (var pos = start; pos < stop; pos += 1) {
    this.notes[pos] = pitches[pitchName];
  }
  if (stop > this.length) {
    this.length = stop;
  }
};

Square.prototype.dsp = function(pos, t) {
  if (pos in this.notes) {
    var tone = this.notes[pos];
    return this.gain * Math.round(Math.sin(2 * Math.PI * t * tone));
  }
  return 0;
};

var melody = new Square(0.2);
melody.addNote('E4',  4, 4);
melody.addNote('F4',  8, 2);
melody.addNote('F4', 12, 2);
melody.addNote('G4', 14, 2);
melody.addNote('G4', 18, 2);
melody.addNote('G4', 22, 2);
melody.addNote('A4', 24, 2);
melody.addNote('B4', 26, 2);
melody.addNote('C5', 28, 2);
melody.addNote('E4', 30, 2);
melody.addNote('E4', 36, 4);
melody.addNote('F4', 40, 2);
melody.addNote('F4', 44, 2);
melody.addNote('G4', 46, 2);
melody.addNote('G4', 50, 2);
melody.addNote('G4', 54, 2);
melody.addNote('F4', 56, 2);
melody.addNote('E4', 58, 2);
melody.addNote('D4', 60, 2);
melody.addNote('E4', 62, 2);

var bass = new Square(0.2);
bass.addNote('C3',  0, 2);
bass.addNote('C3',  6, 2);
bass.addNote('D3',  8, 2);
bass.addNote('D3', 14, 2);
bass.addNote('E3', 16, 2);
bass.addNote('E3', 22, 2);
bass.addNote('F3', 24, 4);
bass.addNote('B2', 28, 4);
bass.addNote('C3', 32, 2);
bass.addNote('C3', 38, 2);
bass.addNote('D3', 40, 2);
bass.addNote('D3', 46, 2);
bass.addNote('E3', 48, 2);
bass.addNote('E3', 54, 2);
bass.addNote('D3', 56, 4);
bass.addNote('B2', 60, 4);

var instruments = [melody, bass];

// calculate song length
var songLength = 0;
instruments.forEach(function(instrument) {
  if (instrument.length > songLength) {
    songLength = instrument.length;
  }
});

function dsp(t) {
  // calculate beat in eighth notes
  var bpm = 100;
  var beat = Math.round(t * (bpm / 60) * 8) % songLength;

  var tone = 0;
  instruments.forEach(function(instrument) {
    tone += instrument.dsp(beat, t);
  });
  return tone;
}