I have a measured FRF by impact testing and I have computed the IRF by ifft(). Now I want to compute the inverse IRF. I have read many posts in this forum about inverting FIR filters. As far as I understood, I must check where are my poles and zeros to see if my inverted FIR filter will be causal and stable. My initial idea was just inverting my FRF and computing again the corresponding IRF (inverse) by ifft(). Then, my poles become zeros and vice versa. When I do this I see that the inverse looks non-causal and quite noisy. Therefore, I want to check the zeros and poles. Here comes my first question:
- How do you compute the zplot in Matlab from an FIR filter coming from a measurement?
My second question:
- In this thread (https://www.dsprelated.com/showthread/comp.dsp/24411-1.php) I read that the inverted FIR filter might be longer (answer from Patrick Gaydecki). Why?
My third question, related to the second question:
- Somewhere else I read that my inverted FIR might become an IIR. Is that true? And Why? Maybe that's why my inverted FIR becomes "longer".
I know there are other methods to compute the inverse FIR, (e.g. LMS inverse), but I want to try this method first.
Thank you in advance for your answers :)