5.1.1 Frequency Response Phase and Group Dela Ideal lowpass filter (zero phase) e-ae生 e8 0,o4o昨元 linear phase a,-s1ng”,o<n< no phase distortion Infinite,computationally unrealizable 元n Noncausal,physically unrealizable sin@(n-na)oo<n<c windowed hp[n]can be causal, π(n-na) 1H(e) e.g.0≤n≤20，n=l0 -2π 0 π 2元 185.1.1 Frequency Response Phase and Group Delay ◆Ideal lowpass filter (zero phase) ( ) j H e  − 2 − −c 0 c  2 1   sin , c lp n h n n   = 18 −    n       k y n x k h n k  =− = −  windowed hlp[n] can be causal, . . 0 20, 10 d e g   = n n •no phase distortion •Infinite, computationally unrealizable •Noncausal, physically unrealizable ( )  ,| | , 0, | | j c lp c d j n H e  e       −  =   ( ) ( ) ( ) sin , d d c lp n h n n n n   − = − ( )  , | | , 0, | | j 1 c lp c H e        =  −    n linear phase