| 摘要 |
PURPOSE:To accurately measure the frequency characteristics of a small amplitude signal and to correctly evaluate the reproducibility of a detailed image or an SN ratio by executing recording/reproducing by a signal superposed by a random noise and measuring noise spectrum. CONSTITUTION:The noise spectrum of a signal obtained by superposing a white noise based on a noise generating circuit 2 to a 50% while noise generated from a video signal generating circuit 1 is measured to obtain a curved line (a). The noise spectrum is supplied to a recorder 100 through a change-over switch 4 and recorded in a magnetic tape T. A noise component of reproduced outputs from noise reduction circuits 110, 120 is removed by an averaging circuit, only the noise component is outputted from an adder 16 and a curve (b) is obtained from a level displayed by a spectrum analyzer 18. Thus, the reproducibility or the SN ratio can be correctly evaluated by calculating the differences between the curves (a) and C and between (b) and (c).
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