def getPrefilter(self,chn):
        """
        Returns the prefilter of signal chn ("HP:0.1Hz", "LP:75Hz N:50Hz", etc.)

        Parameters
        ----------
        chn : int
            channel number

        Examples
        --------
        >>> import pyedflib
        >>> f = pyedflib.data.test_generator()
        >>> f.getPrefilter(0)==''
        True
        >>> f._close()
        >>> del f

        """
        if 0 <= chn < self.signals_in_file:
            return self._convert_string(self.prefilter(chn).rstrip())
        else:
            return self._convert_string('')
Returns the prefilter of signal chn ("HP:0.1Hz", "LP:75Hz N:50Hz", etc.)

        Parameters
        ----------
        chn : int
            channel number

        Examples
        --------
        >>> import pyedflib
        >>> f = pyedflib.data.test_generator()
        >>> f.getPrefilter(0)==''
        True
        >>> f._close()
        >>> del f