function fractalNoise(x, y, frequency, octaves, persistence = 0.5, lacunarity = 2) {
  let total = 0;
  let amplitude = 1;
  let maxValue = 0; // Used for normalizing result to 0.0 - 1.0

  for (let i = 0; i < octaves; i++) {
    total += noise2D(x * frequency, y * frequency) * amplitude;
    maxValue += amplitude;
    amplitude *= persistence;
    frequency *= lacunarity;
  }

  return total / maxValue;
}