Multirate Filters : An Overiew

The multirate filtering techniques are widely used in sampling rate conversion systems, and for constructing filters with equal input and output rates. Various multirate design techniques provide that the overall filtering characteristic is shared between several simplified sub-filters that operate at the lowest possible sampling rates. Design constraints for sub-filters are relaxed if compared to a single rate overall filter. Hence, by using the multistage approach, the total number of coefficients is significantly reduced. As a consequence of the reduced design constraints, the effects of quantization (finite word-length effects) in sub-filters are decreased. Multirate filters provide a practical solution for digital filters with narrow spectral constraints that are very difficult to solve otherwise.