| 摘要 |
PURPOSE:To enable to make a clear call even under high noisy state, by providing a variable loss circuit between a microphone amplifier and an audio switch and a variable gain amplifier between an amplifier for speaker and an audio switch. CONSTITUTION:Noise around telephone sets 1 and 2 passes through amplifiers 7, 8, 44, and 49, rectifying circuits 45 and 50, and smoothing circuits 46 and 51 from microphones 3 and 4 and is inputted to subtraction circuits 47 and 52. The output of the circuits 47 and 52 is logarithmically converted at logarithmic amplifiers 54 and 55 and applied to a subtraction circuit 56 to control variable loss circuits 41 and 42 and variable gain amplifiers 42 and 43. Thus, the audio signal and noise outputted from a speaker 5 and inputted from the microphone 3 are subject to a suitable loss to increase articulation and the audio signal inputted from the microphone 4 and outputted from a speaker 6 is increased for the gain and the signal can be listened to clearly even under high noisy state. |
