Abstract: An EMC filter for a balanced multi-wired telecommunication line has an oblong closed magnetic path core 50 having at least one first core arm 50a with a first length and second core arms 50b with a second length which is equal to or shorter than the first length, and a plurality of coils 51 constituted by at least one pair of wires. The at least one first core arm 50a and the second core arms 50b constitute a closed magnetic path. The wires of each pair are closely positioned each other and wound around the at least one first core arm 50a so as to produce magnetic fluxes in the first core arm 50a flowing toward the same direction when a common-mode current flows through the wires. Each of the coils 51 has a signal input end and a signal output end, and the wires run in a one-way direction from the signal input ends to the signal output ends, respectively.

Abstract: In the loudspeaking telephone circuit, the speech signal is used as a control signal for detecting the extent of decreasing the acoustic coupling between the loudspeaker and the microphone of the telephone set and of the coupling between the transmitting and receiving circuits of an anti-sidetone circuit from an expected worst condition for which the telephone circuit has been designed thereby automatically decreasing the value of the variable loss utilized for preventing howling by an amount corresponding to said decrease. This circuit provides satisfactory speech communication with a smaller loss inserted than a prior art voice switch thus greatly improving unnatural sound as caused by the voice switch.