| 摘要 |
PURPOSE:To prevent generation of transient noises by starting and releasing the muting operation always at a zero cross point of a signal waveform to attain high-speed muting. CONSTITUTION:When a muting commanding/releasing switch 48 is close, the level of an input terminal of an AND circuit 46 goes to a high level by a voltage drop across a resistor 52 during the closed period. The zero cross point or the vicinity is detected from an output waveform of a buffer circuit 8 and a zero cross detecting circuit 18A produces as output. As a result, a high-level output is generated while a waiting the incoming of the zero cross point of the signal waveform when the switch 48 is closed and a muting switch 12 is opened.
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