Digital Two-Rate IIR and Hybrid IIR/FIR Filters for Sampling Rate Conversion

Abstract

The paper discusses structures, design methods, and efficiency of digital two-rate filters for sampling rate alteration by integer or rational ratios. Four canoic filter structures are demonstrated: the direct form, the parallel form, the ladder/lattice forms, and a structure based on canonic all-pass sections. In addition, a structure exploiting numerator coefficient symmetry is presented. An extended class of filters (hybrid IIR/FIR) where the passband equalization is performed by a combination of poles and off-the-unitcircle zeros is introduced. We also describe a design method which iteratively utilizes the Remez algorithm. This simple extension of the McClellan et al. program [24] facilitates the design of virtually any kind of filter including hybrid filters and/or two-rate filters. Several design examples are presented to visualize the different aspects of two-rate filtering.