Speeds up convergences and reduces ringing by increasing the size of the SNR mask without introducing noise
"flt.zero_snr"
, then the basic mask created by thresholding at the SNR value specified by flt.zero_snr is modified by
expanding each un-masked " source" area down to an SNR equal to flt.zero_snrlo, without introducing any
new isolated source areas. The flt.zero_snrlo should be lower than the flt.zero_snr value. [0]