Improved threshold adaptation is provided for a predefined pattern in data. A detection threshold employed by a Euclidean detector to detect a pattern (such as a Servo Address Mark) in data is adapted by determining a minimum Euclidean distance metric Dp before the pattern is declared in a given portion of the data; determining a Euclidean distance metric Ds at a time when the pattern is found in the given portion, wherein at least one of the patterns is found using a Hamming detector; determining, for a plurality of the portions, a minimum Dp value, Dpmin, that is a substantial minimum Dp value for the plurality of portions and a maximum Ds value, Dsmax, that is a substantial maximum Ds value for the plurality of portions; and determining the detection threshold based on the minimum Dp value, Dpmin, and the maximum Ds value, Dsmax. The detection threshold is optionally based on a configurable margin gain value.