A method leverages knowledge of the actual or ideal bit sequence to improve the performance of any sequence detector. This improved performance results by constraining the sequence detector when the sequence detector has knowledge of known patterns within the sample sequence. Embodiments may control or limit the effects of ISI on a readback signal in order to allow higher storage within physical media such as that of a HDD. This method involves reading an analog waveform from the physical media. The phase of this analog waveform is determined and it is sampled at regular intervals using a timing recovery scheme. This sample sequence is equalized (filtered) and sent to a sequence detector which will compare the received sequence to all possible transmitted sequences, generating a path through a trellis that represents the estimated sequence. That trellis path may pass through known states at certain times. This knowledge makes it possible to remove some of the paths under consideration. Then the sample sequence may be compared to a reduced set of possible bit sequences to select a decoded bit sequence.