7.2.2 impulse Response of Ideal Filters o The frequency response of the ideal lowpass filter is LP e l≤r The corresponding impulse response coefficients is SIn on LP 0<n< It is doubly infinite, not absolutely summable, and therefore unrealizable7.2.2 impulse Response of Ideal Filters  The frequency response of the ideal lowpass filter is   sin , c LP n h n n n   = −     It is doubly infinite, not absolutely summable, and therefore unrealizable. ( ) 1 0, c j LP c H e          =      ， The corresponding impulse response coefficients is