| 摘要 |
PURPOSE:To prevent the effect of detection delay of double talk from being given onto an adaptive digital filter by using a shift register so as to retard and echo signal and giving the result to a subtractor circuit and providing a delay circuit. CONSTITUTION:Level detection circuits 53, 54 constituting a double talk detection circuit 52 consist of shift registers 53-1, 54-1 and the first Fourier transformation circuits 53-2, 54-2 and a delay circuit 55 is connected to the reception input side of the adaptive digital filter 11. The time after the generation of double talk till the stop of the adaptive control operation is retarded by the shift register 53-1 and the delay circuit 55 so a to prevent the effect of the detection delay of double talk. In this case, since the delay time at the echo signal yl is obtained by the shift register 53-1, it is not required to provide the circuit individually to simplify the circuit constitution.
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