private double[] berechneRechteck(double amp, double freq, int nHarm, int N) {
	  double[] x = new double[N];
      for (double n = 0; n < N; n++) {
          for (double k = 1; k <= nHarm; k++) {

              x[(int) n] += (4.0 * amp / Math.PI)
                      * (Math.sin(2.0 * Math.PI * freq * ((2.0 * k) - 1.0) * (n / N)) / ((2.0 * k) - 1.0));
          }
      }
      return x;
  }