In one embodiment the present invention includes a qualification circuit that controls a read channel in a data storage device. The qualification circuit includes a first circuit and a second circuit. The first circuit receives a first signal and generates a second signal based on a signal quality of the first signal. The second circuit receives the second signal, an envelope-derived error signal resulting from performing envelope derived error detection, and a decision-aided error signal resulting from performing decision aided error detection. The second circuit modifies the envelope-derived error signal and the decision aided error signal according to the second signal. The second circuit generates a control signal that controls the read channel according to the envelope-derived error signal and the decision-aided error signal having been modified.