| 摘要 |
PURPOSE:To eliminate malfunction at the time of AFM recording mode of low recording level and normal recording mode by enabling surely the titled circuit to detect the presence of record of FM aural signals. CONSTITUTION:Envelope detection output SER including drop-out etc. is rectified by a low pass filter 38, and at the same time, this envelope detection output SER is shifted down by the first DC level Valpha set to specified level and used as a reference level VREF. When recording level of FM aural signals is low, the second DC level Vgamma that changes according to noise level including unmodulated noise is superposed on the reference valve VREF to raise the level. Thus, by comparing envelope detection output SER by the reference level VREF shifted down by Valpha, presence of FM aural signals recorded at ordinary recording level can be detected surely. When recording level is low, the reference level VREF becomes high correspondingly, accordingly, FM aural signals can be detected. |
