5.1.1 Ideal Frequency-Selective Filters ◆ Ideal lowpass filter 少<W e -0<n<O ◆ Noncausal,not computationally H realizable ◆ no phase distortion 2丌 丌-W W,丌 2丌 C C5 5.1.1 Ideal Frequency-Selective Filters ◆Ideal lowpass filter ( ) 1, 0, jw c lp c w w H e w w     =      ( ) jw H e 0 − 2 − − wc wc  2 1   sin ,  = −     c lp w n n h n n ◆Noncausal, not computationally realizable ◆no phase distortion