Patent ID: 7173783

Claim:
In a data channel for a data storage device having a magnetic data storage media and a transducer for recording/playback of data on the media, the channel including a detector having multiple states arranged for maximum likelihood decoding of a series of sample bits with pattern dependent noise and nonlinearities to form a series of detected bits, a method of determining branch metrics for branches of a trellis corresponding to the multiple states in the detector, wherein each branch j connects two of the states, the method comprising the steps of: (a) determining an ideal value d j as a function of the corresponding sample bits; (b) determining a difference between the ideal value d j and a sample value y represented by the corresponding sample bits; (c) determining a branch metric scaling factor c j as a function of the noise variance for the corresponding sample bits; (d) generating the branch metric BM as a function of the difference and the scaling factor c j ; and (e) performing read-to-read adaptation of the ideal value d j using statistics accumulated for other d j values read from the media.