Design of discrete coefficient frequency-response-masking FIR digital filters

In this paper, two methods to design frequency-response-masking (FRM) FIR digital filters with discrete coefficients obtained from optimal continuous coefficients are investigated. First, a one-by-one (OBO) quantization from optimal continuous coefficients is described. Then, a novel recursion design (RD) is presented, which reduces computation by searching only possible quantization sequence in next recursion from the minimum magnitude response error in last recursion. To decrease current magnitude response error, the normal quantization is modified by adding an integer multiple of the quantization step value. For a further reduction, a re-optimization is inserted into the recursion procedure. A design example shows that RD can obtain the discrete coefficients with smaller maximum passband magnitude ripple than those using direct quantization (DQ) and OBO; whereas its maximum stopband magnitude ripple is almost identical to that of OBO.