1. An apparatus for locating a sync pattern in a digital data stream, comprising: means, responsive to said digital data stream, for detecting the sync pattern, for generating a first signal in response to a condition in which said sync pattern occurs at a position in said digital data stream within a window about an expected position of said sync signal and for setting a width of said window in accordance with a value of a threshold signal; and means, responsive to said first signal for generating said threshold signal to have (a) a first value causing said window to have a first width in response to a condition in which said first signal occurs within a predefined interval, and (b) a second value causing said window to have a second width greater than said first width in response to a condition in which said first signal does not occur within said predefined interval.