Improve estimate of the common-mode by increasing the size of the SNR
mask without introducing noise COM.ZERO_SNRLO
"com.zero_snr" , then the basic mask created by thresholding at the SNR value specified by
com.zero_snr is modified by expanding each un-masked " source" area down to an SNR equal to
com.zero_snrlo, without introducing any new isolated source areas. The com.zero_snrlo should be
lower than the com.zero_snr value. [0]