I am working on a reverse engineering problem - I am trying to reconstruct a filter.
- The step response of the system. (I could calculate the impulse response by derivating)
- The system consists of a low-pass FIR and a decimation unit (decimation by 4, probably).
- In the step response, there is always a point in the middle of the step amplitude (the attached image)
- The group delay of the entire system is around 68.
- The impulse response should be symmetrical - for all obtained impulse responses (I have acquired several step responses) there are two points with similar amplitude - apart from those two points the impulse response is symmetrical.
- According to the manufacturer, the filter should have 5% skirt and 104 dB attenuation.
My main task is to repeat the behaviour of the system - convolving new signals with the obtained impulse response works - still - I would like to have a model of my filter.
I would like to synthesise a filter (FIR), which similar characteristics - with group delay around 68. (the filter should have more than decimation*68*2 taps)
I cannot obtain a filter which would guarantee this middle point. Could you recommend me a tool/approach? (currently, I'm using the MATLAB filter design tool)
EDIT. I would like to generate several filters and select the best filter. (more Bayesian approach)
Thank you in advance