| 摘要 |
PURPOSE:To clearly discriminate a multi-frequency signal from other sound signals and to reduce an error by making an incoming signal invalid when an integrated value integrated in a narrow frequency band does not go to more than a prescribed rate to an integrated value integrated in a wide frequency band. CONSTITUTION:A decision circuit 7 is newly provided. An output signal of a level adjusting circuit 1 is inputted to integrating circuits 71 and 72. The circuit 71 integrates an input signal in a constant of 1/2sec during a fetching of the input signal in the wide frequency band. The circuit 72 has two resonance filters and integrates the signals of a high group frequency and a low group frequency passing through the filters in a time constant of 1/2sec. The outputs of the circuits 71 and 72 are inputted to a comparison circuit 73 and compared. The circuit 73 transmits an output when the output of the circuit 72 is higher than the output of the circuit 71 to more than a prescribed degree. When the sound is inputted, since the power ratio of the high group frequency component present in the input signal does not go to about a half, an abnormal signal is outputted to an FF 67 and an output signal SP is made invalid. In the case of a PB signal, since said power ratio goes to a half, the circuit 73 outputs a normal signal and makes the signal SP valid.
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