7.0 Introduction Frequency-selective filters pass only certain frequencies Any discrete-time system that modifies certain frequencies is called a filter. We concentrate on design of causal Frequency-selective filters (IIR,FIR). IH(e) 1+81 1-81 He） Passband Transition Stopband -2π-π-0.0 0 p 0e元 2n 44 7.0 Introduction ◆Frequency-selective filters pass only certain frequencies ◆Any discrete-time system that modifies certain frequencies is called a filter. ◆We concentrate on design of causal Frequency-selective filters (IIR, FIR). ( ) j H e  − 2 − −c 0 c  2 1