ALL PASS FILTER & group delay

[pigkiller]

since we can use all pass filter to compensate the group delay of the cascade stage of the low pass filter. I wonder if i can use higher order all pass filters to get better group delay? If we can, what's the defect of using higher order all pass filters?

 

[flatulent]

You can make two types of pole-zero combinations. One is on the real axis and the other is complex pairs. You can use any number of these to get a flat group delay.

 

[Borber]

Requesting smaller GD ripple has consequence of greater order of allpass filter. Higher order allpass means allso greater total delay of filter.
Complex allpass sometimes means more dificult tunning of a filter.