def _get_stddevs(self, C, stddev_types, num_sites):
        """
        Return total standard deviation.
        """
        assert all(stddev_type in self.DEFINED_FOR_STANDARD_DEVIATION_TYPES
                   for stddev_type in stddev_types)

        # Using a frequency independent value of sigma as recommended
        # in the caption of Table 2 of Atkinson (2010)
        stddevs = [0.26/np.log10(np.e) + np.zeros(num_sites)]

        return stddevs
Return total standard deviation.