| 摘要 |
PURPOSE:To easily adjust the volume of a speaker with simple constitution and to obtain stable operation by providing a variable gain amplifier circuit between the transmitting output of an echo canceller that eliminates a line echo signal and the receiving input or the echo canceller that eliminates a room echo signal. CONSTITUTION:The variable gain amplifier circuit 7 is connected between the transmitting output terminal Sout of an echo canceller 5 and the receiving input terminal Rin of an echo canceller 6. In such a way, when a loss M within a round loop in a loud speaking telephone circuit is M<=-p(a fixed value)<=0 (p is near singing condition), the gain of the variable gain amplifier circuit 7 is possible to be raised to a gain A that does not become a condition [howling (singing) quasi-singing] to prevent a call. Also, because each echo path loss is definite, it is possible to identify the operation modes of the echo canceller 5 and 6 and the volume of the call is made variable and also, it is possible to operate steadily until the gain A.
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