How to Decimate with a DSP
The decimation itself introduces aliases, too, so the bandwidth must be further limited. A digital filter can remove those disturbing frequency components, which the analog anti-aliasing filter did not. The best response is achieved with linear phase filters. We discuss the different definitions for the best alias rejection and present algorithms to design the corresponding optimum filters. We investigate the best implementations as well, also when we decimate together with quadrature conversion and digital mixing. Special filter types are examined (comb-, multi-rate-, cascaded half-band filters) and the effects of forcing some coefficients to 0.