This series of four lessons sets the context for the subsequent two series on designing frequency selective filters. You will learn the different types of frequency selective filters and the difference between infinite and finite impulse response (IIR and FIR) filters. You will also learn how group delay characterizes the phase distortion introduced by a filter and how to implement zero-phase filters when all the data to be filtered is already stored. This series will provide insight that helps you master IIR and FIR filter design in the next two series.