Exercise 18 (a).   Construct a filter using the zeros      for "zeroing out"   ,  ,  and  .

Solution 18 (a).

See text and/or instructor's solution manual.

Answer.   Compute the product  

                    .  

The desired filter is  

                    .  

Solution.   Use the conjugate pair of zeros      and   ,  

and the "zero out factors"      and   .  

Then calculate  

                      

This is a basic filter and we can use Property (i) Zeroing Out Filter.  

The transfer function for part (a) has the form  

                      

and corresponds to the filter

                    .  

        For this exercise, we use      and      in these equations to get the desired recursive formula  

                    .  

Therefore, the desired filter for part (a) is

                    .  

We are done.   

Aside.  We can let Mathematica double check our work.

Aside.  The Maple commands are similar  

  

                                                              


  

                                                              

We are really done.   

Aside.  We can graph the amplitude response for the filter   .  

                    Amplitude response   ,   and zero-pole plot of   ,  

                    for the filter   .

                    We can see that some of the high-range frequencies are attenuated, and      for   .  

Aside.  In Exercise 12 (b) we investigated the filter   .  

We are really really done.   

Aside.  For illustration, we can graph the causal input sequence   ,  

and the corresponding causal output sequence   .  

The signal component    will be amplified  by the factor  ,  and  

The signal component    will be attenuated by the factor  .  

                    The causal input sequence      and the corresponding causal output sequence.

                    Here we have     and   
                    
                    This filter reduces the proportion of the signal component      by a factor of   .

This solution is complements of the authors.

(c) 20098 John H. Mathews, Russell W. Howell