1. A method of calibrating a Viterbi detector, said Viterbi detector comprising at least one noise predictive filter, said method comprising: (a) obtaining noise samples in a training phase; (b) averaging said noise samples; (c) estimating entries of a 3-by-3 conditional noise matrix C &lsqb;k&rsqb; defined by 18 C ij [ k ] = E ( n i - 3 &it; n j - 3 | NRZ &it; &it; condition &it; &it; k ) ; and (d) calculating at least one tap of said at least one noise predictive filter based on said estimated entries.