code: def calc_area_under_PSD(self, lowerFreq, upperFreq):
          
          Freq_startAreaPSD = take_closest(self.freqs, lowerFreq)
          index_startAreaPSD = int(_np.where(self.freqs == Freq_startAreaPSD)[0][0])
          Freq_endAreaPSD = take_closest(self.freqs, upperFreq)
          index_endAreaPSD = int(_np.where(self.freqs == Freq_endAreaPSD)[0][0])
          AreaUnderPSD = sum(self.PSD[index_startAreaPSD: index_endAreaPSD])
          return AreaUnderPSD
docs: Sums the area under the PSD from lowerFreq to upperFreq.
  
          Parameters
          ----------
          lowerFreq : float
              The lower limit of frequency to sum from
          upperFreq : float
              The upper limit of frequency to sum to
  
          Returns
          -------
          AreaUnderPSD : float
              The area under the PSD from lowerFreq to upperFreq