ECHO PREVENTION CIRCUIT, DIGITAL SIGNAL PROCESSING CIRCUIT, FILTER COEFFICIENT SETTING METHOD FOR ECHO PREVENTION CIRCUIT, FILTER COEFFICIENT SETTING METHOD FOR DIGITAL SIGNAL PROCESSING CIRCUIT, PROGRAM FOR SETTING FILTER COEFFICIENT OF ECHO PREVENTION CIRCUIT, AND PROGRAM FOR SETTING FILTER COEFFICIENT OF DIGITAL SIGNAL PROCESSING CIRCUIT

摘要

PROBLEM TO BE SOLVED: To effectively prevent echoes by using an adaptive filter provided with such filter coefficients that on the basis of an output signal from a second subtracter circuit, an output signal from an output terminal is an output signal from a first subtracter circuit that has had the other than a second input signal removed or reduced. SOLUTION: An echo prevention circuit comprises: an input terminal; a first and second FIR filters 4, 11 into which a first input signal is inputted through the input terminal; an input/output terminal to which an output signal of the first FIR filter 4 is outputted and the output signal reflected is inputted or a second input signal is inputted; the first subtracter circuit that subtracts an output signal of the second FIR filter 11 from a combined signal of the output signal of the first FIR filter 4 and the second input signal; the adaptive digital filter into which the output signal of the first FIR filter is inputted; the second subtracter circuit that subtracts the output of the adaptive digital filter from the output of the first subtracter circuit. The adaptive digital filter has such filter coefficients that the output signal from the output terminal is the output from the first subtracter circuit that has had the other than the second input signal removed or reduced. COPYRIGHT: (C)2007,JPO&INPIT