| 摘要 |
PURPOSE:To suppress the generation of unpleasant noise to a maximum limit by detecting that the synchronizing signal for television does not exist and muting a voice after a fixed time delay. CONSTITUTION:An IF signal 17 is obtained from a tuner 1 of a television receiver and impressed to a voice detecting circuit 2 and a video detecting circuit 11. When a synchronizing signal is detected 12 from a video signal, a timer 13 outputs a level H immediately, releases a muting signal 14, and when the output of a synchronizing detecting circuit 12 is turned off, the muting signal 14 is outputted after the fixed time delay. A volume control voltage generating circuit 10 D/A-converts 9 the output of an up down counter 7, converts it to a direct current voltage and controls the output of a voice amplifier 3. When the input of the D/A converter 9 comes to be all '0', the output of the voice amplifying circuit 3 comes to minimum, and a speaker 5 comes to the silent condition. Thus, when the synchronizing signal of a video signal is absent, the voice is muted and the tramp of the action of a muting circuit due to the fluctuation of an electric field is prevented.
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