A playback signal processing circuit for reducing decode errors and enabling high-density digital magnetic recording and a digital magnetic recording reproducing unit using the playback signal processing circuit are provided. An estimated waveform generation circuit uses the decoding result of a PRML channel to generate an ideal playback signal waveform. A subtractor provides a waveform representing a difference between the waveform and an actual playback signal. There is a high probability that error bits will occur at an interval of two or four bits because of the nature of GCR code and maximum-likelihood decoding; in the error state of each bit, one bit is incremented by one with respect to the correct bit value and the other signal bit is decremented by one. From this fact, an error detection circuit discriminates an error difference waveform pattern and an error discrimination circuit detects an error bit interval, whereby an error correction circuit carries out error bit correction.
* 5961658 PR4 equalization and an EPR4 remod/demod sequence detector in a sampled amplitude read channel
* 6052248 Parity channel code for enhancing the operation of a remod/demod sequence detector in a d=1 sampled amplitude read channel
6185173 Sampled amplitude read channel employing a trellis sequence detector matched to a channel code constraint and a post processor for correcting errors in the detected binary sequence using the signal samples and an error syndrome
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