Adaptive filter capable of removing a residual echo at a rapid speed

An adaptive filter comprising first through N-th taps, where N represents a positive integer which is not less than one, filter means for filtering a received signal into a filtered signal in accordance with first through K-th controllable tap gains, where K represents a positive integer which is less than the positive integer N, tap selecting means for selecting selected ones of said first through said N-th taps as first through K-th selected taps in accordance with a tap select signal to connect said first through said K-th selected taps to said filter means, and producing means for producing said tap select signal in accordance with said first through said K-th controllable tap gains, wherein:

• each of said first through said N-th taps belongs to either one of first through M-th tap groups, where M represents a positive integer which is less than the positive integer N;
• said producing means comprising:
• first generating means for generating a specific one of said first through said M-th tap groups;
• second generating means for generating said tap select signal in accordance with said first through said K-th controllable tap gains and said specific tap group;
• and
• control means responsive to said tap select signal for controlling said first generating means to make said first generating means generate a renewal one of said first through said M-th tap groups as said specific tap group.