# Conjugate Pole Pairs

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?

Thanks

• your prof was wrong. – robert bristow-johnson Feb 23 '17 at 1:11
• Poles on the unit circle means that the filter is unstable. Maybe your prof was allergic to this :-) – Hilmar Feb 23 '17 at 13:12

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