Low pass filter design

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Bob 2020-11-20

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评论： Star Strider 2020-11-21

Hi,

Is it good Idea to design low pass filters (moving average , FIR filter, Kalman filter, Butterworth and Chebyshev filter) with same filter parameters (cut off frquancy, filter order etc.) for comparision purpose inorder to filter the higer frequancy noise?

For the selction of best filter to filter higher frequancy noise.

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Star Strider 2020-11-20

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My preference would be an elliptic IIR filter for efficiency. See the documentation for ellip for details. For best results, begin with ellipord, and get the [z,p,k] output from ellip, then use second-order-section representation for stability with zp2sos. Use that result with filtfilt to do the actual filtering.

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Star Strider 2020-11-21

The order essentially is the number of delay elements (usually corresponding to the number of poles) in the filter. I prefer higher-order filters, since they have narrower transition zones (and steeper cutoff regions). The order depends on what the filter is supposed to do, in the context of the signal it is supposed to work with.

There is no universal order that works best in all situations. An IIR elliptic filter with an order of about 6 can do as well or better than a FIR filter of a much higher order (perhaps at least 10 times that) to do the same essential operation. However to create a filter with multiple passbands and stopbands, IIR filters would have to be connected in parallel, while one FIR filter would work.

There is no one best answer to this, since applications differ and filter designs to accomplish those applications differ. A second-order IIR filter can work quite well if the requirements match what the filter can do (for example filter out high-frequency noise that is not close to the desired signal in the frequency domain). A second-order FIR filter would likely not perform well, regardless of the application.