| 摘要 |
PURPOSE:To establish the audio communication circuit enabling natural communication, by connecting the circuit recognizing audio and noise before the variable loss circuit for the transmission and reception line with branch, and controlling the restoration delay time circuit with the output. CONSTITUTION:In case of non-communication state, when the reception signal from the line 16 is incoming via the side tone prevention circuit 5, the output of the circuit 12 comparing the output of the rectifying and smoothing 10, 11 is positive. The restoration delay time circuit 13 makes positive the output 15 with comparatively shorter time constants R1.C1, the loss in the transmission variable loss circuit 3a is increased and the loss of the reception variable loss circuit 7 is decreased. When the reception signal starts the attenuation of end of call, although the comparison circuit output 14 is negative in faster time constant, the output 15 of the circuit 13 attenuates in longer time constants R.C1, to avoid the cut off of call end of reception signal. When the transmission signal is inputted in superimposition with the end of call, the noise audio identifying circuit 17 makes negative the outpt 15 of the circuit 13 in shorter time constants R3.C1 to decrease the loss of the loss circuit 3a and to increase the loss of the loss circuit 7. |
