| 摘要 |
PURPOSE:To reset a frequency corresponding to variation and to correct a phase shift by sending out a signal of constant frequency to an echo path for a short time during a break period of a conversation between both callers, and detecting the phase shift due to a frequency offset, etc., at some carrier terminal station on the path. CONSTITUTION:The voice detecting circuit 1 of a carrier terminal station detects whether a receive signal is present or not and sends its detection signal to a tone generator 2. This generator 2 operates a changeover switch 6 when there is no receive signal to send out a constant tone signal to an echo path 7. The tone frequency returning through this path 7 is applied to a phase compensating circuit 3 and an echo signal is applied to the arithmetic circuit 3 of an echo canceler 5 after its phase distortion is compensated. When the echo canceler 5 detects the phase shift of the echo path 7, the frequency corrsponding to the phase shift is returned to the frequency of the original signal and applied to the circuit 3 through an absolute delay circuit 4 to compensate the phase variation. |
