  An optimized digital shaping filter has been developed for the GERDA
experiment which searches for neutrinoless double beta decay in 76Ge. The GERDA
Phase I energy calibration data have been reprocessed and an average
improvement of 0.3 keV in energy resolution (FWHM) at the 76Ge Q value for
0\nu\beta\beta decay is obtained. This is possible thanks to the enhanced
low-frequency noise rejection of this Zero Area Cusp (ZAC) signal shaping
fillter.
