1. A method of demodulating a servo burst signal from a read head of a disk drive, comprising the steps of: oversampling the servo burst signal during each of a plurality of successive time intervals, in order to obtain a plurality of samples for each said time interval; summing the plurality of samples for each said time interval in order to obtain a respective accumulation value for each said time interval; and determining a burst value for the servo burst signal by applying a filtering function to a set of said accumulation values; wherein said time interval is a half cycle of the servo burst signal, and wherein said determining step includes the steps of summing a first group of the accumulation values which correspond to positive half cycles of the servo burst signal and summing a second group of the accumulation values which correspond to negative half cycles of the servo burst signal, thereafter applying the filtering function only to the accumulation values of said first group if said second sum exceeds said first sum by a predetermined amount, and applying the filtering function only to the accumulation values of said second group if said first sum exceeds said second sum by a predetermined amount.