# Problem understanding a parameter in a digital filter

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1. Feb 9, 2019

### diredragon

1. The problem statement, all variables and given/known data
Digital causal recursive filter is a part of a digital signal processing system which has sampling frequency $fs = 1200Hz$ and is given by a differece equation:

where $r = 0.9$ and $θ$ is such that it filters out the spectral components at $f = 200Hz$
Find $H(z)$ and graph the poles and zeros of this filter.

2. Relevant equations

3. The attempt at a solution

I'm having trouble figuring out how to determine the $θ$ in this equation. I did find the $H(z)$ in function of $cos(\theta)$ but still made no progress on determining it. How does the fact that it filters out $200Hz$ help me in this case? Is it something with the location of the zero or a pole on the plane?

2. Feb 14, 2019 at 6:00 PM

### PF_Help_Bot

Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.

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