code: def crop_frequencies(self, low=None, high=None, copy=False):
          
          if low is not None:
              low = units.Quantity(low, self._default_yunit)
          if high is not None:
              high = units.Quantity(high, self._default_yunit)
          # check low frequency
          if low is not None and low == self.f0:
              low = None
          elif low is not None and low < self.f0:
              warnings.warn('Spectrogram.crop_frequencies given low frequency '
                            'cutoff below f0 of the input Spectrogram. Low '
                            'frequency crop will have no effect.')
          # check high frequency
          if high is not None and high.value == self.band[1]:
              high = None
          elif high is not None and high.value > self.band[1]:
              warnings.warn('Spectrogram.crop_frequencies given high frequency '
                            'cutoff above cutoff of the input Spectrogram. High '
                            'frequency crop will have no effect.')
          # find low index
          if low is None:
              idx0 = None
          else:
              idx0 = int(float(low.value - self.f0.value) // self.df.value)
          # find high index
          if high is None:
              idx1 = None
          else:
              idx1 = int(float(high.value - self.f0.value) // self.df.value)
          # crop
          if copy:
              return self[:, idx0:idx1].copy()
          return self[:, idx0:idx1]
docs: Crop this `Spectrogram` to the specified frequencies
  
          Parameters
          ----------
          low : `float`
              lower frequency bound for cropped `Spectrogram`
          high : `float`
              upper frequency bound for cropped `Spectrogram`
          copy : `bool`
              if `False` return a view of the original data, otherwise create
              a fresh memory copy
  
          Returns
          -------
          spec : `Spectrogram`
              A new `Spectrogram` with a subset of data from the frequency
              axis