1. A machine-implemented method for detecting a defect region on a hard drive, the method comprising: (a) the machine generating a first measure based on signal values, x[n] y[n] expected signal values corresponding to the signal values, and soft-decision values L[n] corresponding to the signal values; (b) the machine generating a second measure based on expected signal values and defect-free soft-decision values corresponding to only defect-free regions of the hard drive; (c) the machine comparing the first and second measures; and (d) the machine detecting the defect region based on the comparison of step (c).