Patent ID: 7552157

Claim:
A recursive digital filter implemented in a signal processor working with integers, comprising: a receiving section that receives an input signal; a calculating section that calculates an output signal of a sample n from the input signal based on: an algebraic sum of input and output values of signals sampled at a selected point in time and at previous points in time, to which coefficients characteristic of the filter have been assigned; and a sum of the remainders of integral divisions, for each of said previous points of time, of the corresponding output value by a scale factor, said remainders to which coefficients characteristic of the filter have been assigned, the output values being rounded by the sum of the remainders to the closest integer, whereby the propagation of error amplification is minimized; a changing section that changes a number obtained from rounding to a default integer value that is obtained from dividing an output value by the scale factor based on a number obtained from rounding to a closest integer to a real-number quotient thereof; and an outputting section that outputs the calculated output signal.