def psd(self):
        """
        A pyCBC FrequencySeries holding the appropriate PSD.
        Return the PSD used in the metric calculation.
        """
        if not self._psd:
            errMsg = "The PSD has not been set in the metricParameters "
            errMsg += "instance."
            raise ValueError(errMsg)
        return self._psd
A pyCBC FrequencySeries holding the appropriate PSD.
        Return the PSD used in the metric calculation.