| 摘要 |
PROBLEM TO BE SOLVED: To attain accurate control stable is sound output by limiting the amplitude of an extracted signal in response to the variance of amplitude of the signal and controlling the output of an input signal according to the level of the signal having its limited amplitude. SOLUTION: The sound signals containing noises and inputted to a 1st amplifier 1 of a squelch circuit are amplified, and the noise components are extracted via a 1st BPF 2. These noise components are amplified by a 2nd amplifier 26 and inputted to a variable level amplitude limiter 27. The limiter 27 branches out the signals received from the amplifier 26 to an amplitude limiting part and a rectifying part. The signals which are inputted to the rectifying part are rectified there and then filtered at a filter part. Therefore, the signals received from the amplifier 26 are turned into the entirely smooth signals including the abrupt change in amplitude. Meanwhile, the signals inputted to an amplitude limiting part are limited in terms of their amplitudes with the level of a filtered signal defined as an amplitude limit level. Thus, both entire change and abrupt changes are suppressed for those signals having their limited amplitudes.
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