Filter design resource recommendation

I am new to matlab filter design and I found the help file of matlab is a little not comple. For example, in the help file of Butterworth filter design. it said,

[A,B,C,D] = butter(___) designs a lowpass, highpass, bandpass, or bandstop digital Butterworth filter and returns the matrices that specify its state-space representation.

However I still do not know how to apply the matrices to signal I want to filter after I get the matrices.

Another example is the filter designer (fdatool.) In the file->Export there is option to export as "Object" or "System Object" but I do not know what is the difference between the two options.

I am wondering if there is a general matlab guide for filter design?

Answer 1

[Star Strider]

You appear to be referencing the Signal ProcessingToolbox butter (link) function.

You do not filter with the state space representation of your filter. You must either use a designfilt (link) object, a transfer function, or preferably a second-order-section representation of your filter. Use the filtfilt (link) function to do the actual filtering.

I sent you some example code on the design and implementation of a Chebyshev Type II filter with your previous post, so I refer you to it and will not repost it here. The only changes you would need to make are to substitute the buttord function for the cheb2ord function, and the butter function for the cheby2 function to design and implement your Butterworth filter. The rest of the code remains the same.

For a general introduction, see Filtering Data With Signal Processing Toolbox Software. There are related discussions available as links on the Digital Filtering page.