| 摘要 |
PURPOSE:To prevent the deterioration of quality of call due to level contrast, by controlling the gain of a variable gain amplifier connected to the reception input of an echo erasing circuit through the output of a detection circuit estimating the amount of erasion of echo. CONSTITUTION:When a signal comes from two-wire side of a direction E, an echo erasing circuit 12 of a direction W is operated, the amount of echo at W transmission side is erased and the amount of erasion is calculated with an echo erasing amount detection circuit 20 and the gain is increased by the amount of erasion for a variable gain amplifier circuit 5 at the E transmission side. When a call only from the W side is made from this state, an echo erasing circuit 11 at the E side is operated and gain direction control of the circuit 5' at the E side transmission side is made and it is operated as two-wire bidirectional amplifier. Thus, in a line having much loss, the voice with a gain from the original call is delivered to the opposing party and it is not required to obtain a greater loss to the opposing side. |
