5.1.1 Frequency Response Phase and Group Delay delay distortion is a rather mild form of phase distortion,its effect is to shift the sequence in time. we accept a linear-phase response rather than a zero phase response in designing filters by method of approximations to ideal filters Ideal lowpass filter with linear phase delay is better ue-本2e四设apgn Hp(e） The impulse response(delayed by time nd) (sing( 元(n-nu -00<1n<00 Ht四相=9 windowed hpl[n]can be causal,,e.g.0≤n≤20，n=l0 175.1.1 Frequency Response Phase and Group Delay ◆Ideal lowpass filter with linear phase delay is better ( )  ,| | , 0, | | j c lp c d j n H e  e       −  =   ◆delay distortion is a rather mild form of phase distortion, ◆The impulse response (delayed by time nd ) its effect is to shift the sequence in time. 17 in designing filters by method of approximations to ideal filters . windowed hLP[n] can be causal, ( ) ( ) ( ) sin , c d lp d n h n n n n n   − = −  − we accept a linear-phase response rather than a zero phase response . . 0 20, 10 d e g   = n n ( )  , | | 0, | | j 1 c lp c H e        =  