At this point the baseband signal is digitally sampled to convert it to a simpler form for correlation. In VLBI, the digital signal is recorded on tape along with accurate time information. In connected element interferometry, the digital signal goes directly to the correlator.

The correlator removes the Doppler shift and geometric delay due to the position and motion of the X and Y stations and then cross-correlates them.

Information provided by: http://www.drao.nrc.ca