| 摘要 |
PURPOSE:To ensure the identification of monaural/stereo in a short time, by providing a means counting a pilot signal. CONSTITUTION:A pilot signal P separated at a filter 11 is converted into a rectangular wave at an LPF11 and the level is adjusted at resistors 28A, 28B, then it is applied to a counter 21 and a control pulse generating circuit 30. When the counter 21 counts it for a prescribed number, the 1st control pulse S1 is outputted. The circuit 30 has a time constant circuit 33 and the cathode side of a diode 32 is at H while the pilot signal P is obtained, and when the pilot signal P is absent and the level is lower than the threshold level (about 1/2 of the peak level of the pilot signal P) of an inverter 31, the output of the inverter 31 is inverted to produce an output SP2. An output SM of a mode switching pulse forming circuit 22 continues from the generating time point of the pulse SP1 to the time point of production of a SP2. The changeover of monaural/stereo is made with the signal SM. |
