The decoded picture quality of HDTV codec for digital VTRs is evaluated when the input picture is at low S/N. The codec scheme is based on JPEG and compresses the HDTV signal to a 90Mb/s data rate. Computer simulations are used for the evaluation. It is found that noise pattern on the decoded picture has been different from the input picture, however the S/N is almost the same. This results in maximum 3dB degradation in subjective assessment. It is also found the noise reducer applied to input picture is effective in low S/N picture coding.

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In digital magnetic recording, bit densities is limited by peak-shift or S/N ratio. In either case, limitations are caused by bit-interferense and discrimination of fixed threshold. Compensation of many bits interferense by viterbi detection may be difficult due to complex algorithm. However, neural network can recognize patterns having complex algorithms without programming. Therfore, if readback waveform is recognized by neural network as several bit patterns after learning of readback waveforms. It may be possible to obtain the higher bit density over the limitation of usual method, because learning of waveform include interferense algorithm and compensation effects. Results of software simulation are discussed.

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An equalizing and detection method using Partial Response Class 4(PR4) was studied utilizing data obtained from a signal generated by a digital VTR for experimental use in a computer. After the dipulse response was computed from reproduced signal, the transversal filter coefficients necessary for equalizing reproduction were obtained by applying a LMS algorithm for the dipulse response waveform. Then, a method was devised for configuring a nonlinear canceller for PR4 which requires no initialization. Finally, when the Viterbi decoder and a nonlinear canceller were combined, it was discover- ed that the error rate was one tenth the standalone Viterbi decoder.

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This paper describes the small size deck mechanism and high density recording technology for home-use digital VCRs. Experiments performed by using this mechanism and metal evaporated tape of 7〜9 μm thickness and 1/4 width yielded the following conclusions. (1) New tape transport system suitable for thin tape has been developed, and track lineality is no more than 3 μm. (2) Small size cylinder of 20 mm diameter has been developed. A shape of head-base suitable for combination-heads has been realized, and leakage magnetic flux around these heads is 0.001 tesla. (3) In recording and playback. CN-Ratio is 47dB( RBW:100KHz ).

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