In this lesson you will learn the characteristics of the four continuous-time or analog filters that are used as a starting point for discrete-time IIR filter design. The four filter types are Butterworth, Chebyshev I, Chebyshev II, and elliptic filters. They differ in the nature of their passband and stopband characteristics. Choosing one of these four filters is the first step in IIR filter design. Understanding the characteristics of these filters will enable you to design effective filters for your application.