We thought that the modulation noise neighbored on carrier might influence the error rate in digital VTR's (Video Tape Recorders). we analyzed the reproduced signals for some tapes made from several magnetic materials using a Noise State Evaluation Function which we define in this paper. We recognized that the total noise of the reproduced Signal is Separated into the modulation noise neighbored On carrier and additional noise which exists in the other region. Based on this analysis, a noise function model of the reproduced signal was considered. Assuming that the maenetic recording channel is linear, the error rate in digital VTR's was calculated using this noise function model. Consequently, we are confident that the modulation noise neighbored on carrier influences the error rate in digital VTR's.

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It is well known that decreasing the thickness of a magnetic layer is effective for high density recording. By using the simultaneous double layer coating method, the magnetic layer of metal particulate tape can be thinned to sub-micron thickness. This paper reports the effects of the very thin magnetic layer thickness on some digital recording performances. As a result, it was shown that reducing the magnetic layer thickness to below 0.4μm was effective for high density digital recording.

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For high-density digital recording with a metal Particulate tape, to lower the self-demagnetization loss in a short-wavelength region by thinning the magnetic layer has proven effective. To estimate the magnetic layer thickness suitable for high-density digital recording, we study the self-demagnetization loss and the thickness loss versus magnetic layer thickness, and measure the recording/reproduction characteristics of the trial MP tapes which have different magnetic layer thicknesses with a D-3 VTR. As to the results, it is found that as the magnetic layer becomes thinner, the self-demagnetization loss becomes lower faster below a magnetic layer thickness of 0.5μm, and the loss is lowered approximately 0.8dB by thinning the magnetic layer from 3μm to 0.18μm. Furthermore, it has been proven that the magnetic layer thickness which does not degrade the S/N ratio of the playback-equalized signal is some 0.2μm or more.

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