I am currently studying for an exam for a Speech Processing course I am taking and stumbled across this question in one of the sample exams:


I began to plot the pole-zero configuration placing my poles on the unit circle at points +j and -j as well as placing my zero in the 0.5 location.

When I compared my plot to his, I noticed that he placed the poles instead in the halfway point of the Imaginary axis and was wondering why he decided to place them there?

Here is my professors answer:



  • 1
    $\begingroup$ your prof was wrong. $\endgroup$ Feb 23, 2017 at 1:11
  • $\begingroup$ Poles on the unit circle means that the filter is unstable. Maybe your prof was allergic to this :-) $\endgroup$
    – Hilmar
    Feb 23, 2017 at 13:12

1 Answer 1


If the dotted-line circle is the unity circle and both the real and imaginary axis are on the same scale, then your professor's answer is wrong.

Your solution is the correct one. It would be something like this:

enter image description here

where the dotted-line circle has a radius $r=1$.

  • $\begingroup$ Thanks for the clarification. Thought I was going crazy for a second $\endgroup$
    – User 5842
    Feb 23, 2017 at 1:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.