static double autocorrelation(double[] voiceSample) {
  int n = voiceSample.length;
  double sum = 0;
  for j to n: {
    double correlation = 0;
    for i to n:
      correlation += voiceSample[i] * voiceSample[mod(i - j, n)];
    sum += correlation;
  }
  ret doubleRatio(sum, n);
}