| 摘要 |
PURPOSE:To guarantee the adaptive operation of an adaptive digital filter by applying subtraction or addition between a present value and a value before T sec as to a difference signal and detecting the polarity of the difference or addition. CONSTITUTION:R-set of sample-and-hold circuits SH1-SHR input a difference signal being an output of a subtractor 10, each sample position is equal and the circuits sample and hold an input signal at T/R sec each. The said difference signal is outputted with a delay of T sec from the SHR and fed to a subtractor 16 at T/R sec each. Thus, the difference between the present sample value and the sample value before T sec appears at an output of the subtractor 16 at T/R sec each. On the other hand, a difference of the residual echo between the present value and the value before T sec is outputted from the subtractor 16 as a residual echo component. In such a case, the residual echo before T sec is regarded as a random noise. The amplitude distribution of the value is symmetrical in positive and negative directions, and the probability where the amplitude (d) is in the relation of ¦d¦<=delta (where; 0<=delta) has a positive value. Thus, the probability where the polarity of the present residual echo is outputted accurately by a polarity detector 12 has a positive value. |
