A sample integrity test is disclosed. The sample integrity test receives an error signal and a defect signal. If the defect signal indicates the presence of a defect, a low-pass filtered error signal is substituted for the error signal. The low-pass filtered error signal is the error signal filtered with a low-pass filter. The error signal can be derived from optical signals from an optical pick-up unit. A control signal generated from the output signal from the sample integrity test controls the position of the optical pick-up unit. The defect signal can also be derived from the optical signals.