The simplest implementation of an FIR filter is based on the direct transversal forms presented in Chapter I, Figures 1.14 and 1.15. When used as an antialiasing filter in decimators or as an antiimaging filter in interpolators, the direct implementation filter structures can be modified to the computationally efficient implementation forms. In this section, we present the efficient decimators and interpolators that provide the arithmetic operations to be evaluated at the sampling rate of the low-rate signal.
Factor-of-M decimator with FIR filter