A data discriminating unit includes a data discriminator and a sync signal discriminator. A data sync signal is detected for the bit string discriminated from the output of the sync signal discriminator, and the data is demodulated for the bit string discriminated from the output of the data discriminator, thereby optimizing the signal to a form suitable for discrimination and detection of the data sync signal and demodulation for data reproduction. As a result, the detection performance of the data sync signal can be improved while maintaining the data discrimination performance. A Viterbi decoder is used for discrimination by the data discriminator and the sync signal discriminator for the optimization thereby to optimize the number of states, the number of paths for state transition and the path memory length. A signal having no continuous inversions of the recording data is used as the data sync signal.

Methods and apparatus are disclosed for detecting PR4 equalized Gray codes, providing phase tolerant Gray codes and detection thereof. A Gray code detector is provided, which receives a PR4 equalized Gray code input signal and provides a binary detector output. The detector comprises a plurality of filters providing Euclidean distance values based on the input signal. A logic component selectively provides the detector output based on one or more of the Euclidean distance values from the matched filters, according to one or more criteria, such as the detector mode.

A PRML detector includes a waveform equalizer for equalizing a waveform of a reproduction signal obtained by reproducing marks and non-marks recorded on a recording medium, and a decoder for generating binary-coded data of the reproduction signal based on the waveform equalized by the waveform equalizer. The decoder outputs a temporary data string which is obtained before the binary-coded data is obtained. The waveform equalizer includes an equalizer that includes a delay element that delays propagation of the reproduction signal, a plurality of multipliers that multiply predetermined coefficients by the reproduction signal and the delayed signal from the delay element, and an adder that adds outputs from the plurality of multipliers. A target value judger determines a target value for equalizing based on the temporary data string output from the decoder and a coefficient adaptive controller calculates the predetermined coefficients and adaptively updates the calculated predetermined coefficients for each of a plurality of multipliers.

A waveform equalizer for equalizing a waveform of a reproduction signal. A delay element delays a propagation of the reproduction signal. A plurality of multipliers multiply predetermined coefficients by the reproduction signal and the delayed propagation reproduction signal. A detector detects an asymmetry of the reproduction signal arising from physical profiles of each of the marks and the non-marks, and outputs a detection signal representing an amount of asymmetry. A discriminator outputs a discrimination signal in response to a discrimination of the marks and the non-marks. A calculator calculates a first coefficient multiplied by the reproduction signal of the marks based on the outputted detection signal, and calculates a second coefficient multiplied by the reproduction signal of the non-marks. A selector selects either the first or second coefficient, based upon the outputted discriminating signal.