Viterbi detector with added noise detection channel

Summary form only given. Media transition noise in disk drives can be comparable to electronic noise, and media design compromises are made to minimize it (K.E. Johnson, J. Appl. Phys., vol. 87, no.9, pt.1-3, pp. 5365-70, 2000). However, its presence also "signals" that a bit transition is present. By separating the noise signal from the signal+noise signal, a noise metric can be added to the normal PR Viterbi metric, potentially lowering the channel error rate. The proposed noise channel signal is taken just before the PR lowpass filter, then passed through a bandpass filter from Nyquist f/sub n/ to 2f/sub n/ (or up to the media grain size noise limit). If the playback signal has little energy above f/sub n/ or if it is close to a PR shape, the transition noise n/sub z/ will dominate in the second channel (termed the noise z-channel). The channels are separately sampled.