ECHO CANCELLING TYPE CONFERENCE TALKING EQUIPMENT

摘要

PURPOSE:To prevent deterioration of S/N when plural microphones are in use by controlling only the attenuation of a variable loss circuit in the highest level channel to 0dB and others to a prescribed attenuation. CONSTITUTION:A respective output signal at the sending side of the 1st-3rd echo cancelling circuits 10-12 is fed to variable loss circuits 17-19 provided respectively and the output at sending side of the 1st-3rd echo cancelling circuits 10-12 is detected and compared. Only the attenuation of the variable loss circuits 17-19 of a channel of the highest output level is controlled to 0dB and the other attenuation of the variable loss circuits 17-19 of the other channels is controlled to a prescribed value. Then outputs of the variable loss circuits 17-19 are added by an adder circuit 23 and sent to the remotest end and the 4th echo cancelling circuit 24 cancels a detour signal produced by a 2/4-wire converting circuit 25.