| 摘要 |
PURPOSE:To attain a call at the optimum level, by providing a variable loss circuit to the output side, controlling the circuit from a high to a low loss when the output of the voice level detecting circuit exceeds a preset threshold value and controlling the threshold value in response to the normal noise level. CONSTITUTION:An output side of a microphone preamplifier P is provided with avariable loss circuit L1, a voice level detecting circuit V, and a normal noise level detecting circuit VT. The circuit V is provided with a variable loss circuit L2, which is controlled from a low to a high loss in proportion to an output of the circuit VT. The circuit L1 is controlled stepwise from a high loss to a low loss at a preset threshold value with the output of the circuit V, and the setting of the threshold value is changed in proportion to the loss of the circuit L2. Thus, independently of the low or high level of the normal noise, sharp gain switching is attained and the malfunction due to normal noise such as voice switch of speaker telephone is prevented and a smooth call is attained. |
