Exercise 17 (b).   Construct a filter using the poles      for boosting up signals near    and    and low frequency signals.  

Hint.  This is similar to Example 9.25 (b).  

Solution 17 (b).

See text and/or instructor's solution manual.

Answer.   Compute the quotient  

                    .  

The desired filter is  

                    .  

Solution.   Use the conjugate pair of poles      and   ,  

and the "boost up factors"      and   .  

Then calculate

                      

Extending the Boosting Up Filter one more term we see that the transfer function

                    ,  

will correspond to the filter

                    .  

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

                    .  

Therefore, the desired filter for part (b) 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   ,  

                    We can see that some of the low-range frequencies are slightly amplified.

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