SIDE TONE LEVEL CONTROL SYSTEM OF ANTI-SIDE TONE CIRCUIT

摘要

PURPOSE:To keep the side tone at an optimum level with the proper timing by using an action start indication signal excepting those signals obtained by application of a power supply to start an action to obtain the side tone level of a control part. CONSTITUTION:A control part 15 includes a microcomputer and obtains B/A and C/A in the form of side tone levels, where the inputs given from signal lines 14, 12 and 13 are defined as A, B, C respectively. Then the part 15 delivers a control signal from a signal line 17 to control a variable impedance balanced circuit network 8 to obtain plural prescribed impedance values and obtains C/A of each impedance. The side tone levels thus obtained are all stored and all side-tone levels are finally obtained. The part 15 compares these levels with each other and delivers a control signal through the line 17 when the minimum level is obtained in the C/A. Then the network 8 is controlled to obtain the corresponding impedance value. In addition, the part 15 delivers a control signal through a signal line 18 to turn on a switch 19 and off a switch 20 respectively.