1. A method for use in detecting an input data stream via a Viterbi system, said method comprising the steps of: providing a Viterbi detector capable of receiving input data samples and converting said input data samples into a digital output signal indicative of data stored on a recording medium or transmitted over a communication channel, said Viterbi detector comprising a trellis structure including: a plurality of nodes arranged in a plurality of rows and columns, each row associated with a distinct state of said Viterbi detector and each column associated with a distinct level of said Viterbi detector; a plurality of state metrics, each state metric associated with one of said distinct states of said Viterbi detector; and a plurality of paths between nodes in adjacent levels in said Viterbi detector, each path having a corresponding transition reference value; tuning a transition reference value associated with a first path of said trellis structure by changing said transition reference value from a first value to a second value, said first path beginning at a state in a first level and terminating at a state in a second level; calculating a transition metric for said first path using said second value of said transition reference value and at least one of said input data samples; combining said transition metric corresponding to said first path with a state metric corresponding to said beginning state in said first level to update said state metric associated with said terminating state in said second level; and choosing a most likely path through said trellis structure using said updated state metric, said most likely path being representative of said digital output signal; wherein said step of tuning improves the error rate performance of said Viterbi detector.