a method of enhancing the signal to noise ratio of seismic data includes the steps of repeatedly obtaining , from at least one array of seismic detectors , analog signals representative of sensed vibrations or pressure waves . each analog signal is converted to discrete digital values on a time correlation basis until a predetermined quantity of analog signals have been converted . in each time correlation , the two most positive digital values and the two most negative digital values are removed . the remaining values for each time correlation are averaged so as to provide a digital representation of the analog signals .