| 摘要 |
A technique is disclosed, which can shorten attack time and release time without using RC filter with time constant. According to this technique, diodes 51 and 52 rectify AC signal at output stage of an amplifier 30 by voltage doubler rectification, and a smoothing capacitor 53 smoothens the signals rectified by the diodes 51 and 52 . A transistor 41 of an attenuation circuit 40 turns on when DC voltage smoothened by the smoothing capacitor exceeds a predetermined level, and level of the output signal of the amplifier is attenuated by drawing the input signal of the amplifier.
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