| 摘要 |
A digital echo canceller has a receive path (2) and a send path (3) and comprises combining apparatus (10) for forming a send output signal (r(k)) as the difference between the signal (z(k)) applied to the send input (SI) and a replica signal (e(t)) used for cancelling an additive echo signal (e(k)) at the send input (SI) that has developed in response to a receive input signal (x(k)) applied to the receive input (RI), which echo canceller at least includes transforming apparatus (13, 15) for transforming the receive input signal (x(k)) and the send output signal (r(k)); transforming apparatus (14) for transforming the replica signal (e(k)); a digital adaptive filter (9) which has a number of filter coefficients for generating the replica signal (e(t)) in response to the receive input signal (x(k)) and the send output signal (r(k)), adaptation apparatus (12) for determining for each block m, adaptation components (A(p;m)) for each of the filter coefficients (W(p;m)) in response to the receive input signal (x(k)) and the send output signal (r(k)); controllable gate means (17) for selectively passing the adaptation components (A(p;m)) to the adaptive digital filter (9); control apparatus (25-28, 21-24, 16) for determining respective levels of the send output signal (r(k)) and the receive input signal (x(k)) and for generating a control signal for the gate apparatus (17) in response to the levels thus determined, which control signals depend in a predetermined manner on the difference between the levels concerned.
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