MATLAB：IIR 滤波器系数

Question

I am fairly new in signal processing, and one of my projects is to implement a C++ filter class. I need the higher order coefficients of typical filters such as Chebyshev types I and II, Butterworth, Elliptic, and unfortunately, most of the coefficient tables in the net only lists up to 10th order max. I decided to use MATLAB to generate these filters and get their higher order coefficients, however one thing that I'm confused about is that they only give out 1 set of coefficients, which I assume to be analogous to saying (ao,a1,a2.....an).

I learned that IIR filters have 2 sets of coefficients, usually expressed as a0,a1...an and b0,b1,...,bn. Here is my MATLAB code to generate these coefs and export them to an excel file:

 %Chebyshev Filter Coefficients

 filename = 'cheby2coefs.xlsx';
 for Order = 1:64 
 fprintf('This is');
 disp(Order);
 fprintf('coefficients');
 [i,j] = cheby2(Order, 20, 300/500);
 disp([i,j]);
 fprintf('\n');

  xlswrite(filename,[i,j]',Order);
end

So far there has been little sources on the net on how to come up with these coefficients with MATLAB, so I'm having a hard time. My question is that, how exactly does one produce the IIR coefficients for these filters (Assuming they're IIR)?

Answer 1

It looks like you're on the right track. Your call to cheby2 is missing the Wst parameter (the stopband frequency). You should read MATLAB's official documentation for this command and verify your call.

Also, don't name the output variables i and j , it's bad practice. i and j are reserved names for the sqrt(-1) imaginary number. Name the output variables b and a at least.

Once you're done with Chebyshev, use butter and ellip for the Butterworth and elliptic filters, respectively.

Answer 2

This seems to be covered in the MATLAB documentation :

[b,a] = cheby2(n,R,Wst) designs an order n lowpass digital Chebyshev Type II filter with normalized stopband edge frequency Wst and stopband ripple R dB down from the peak passband value. It returns the filter coefficients in the length n+1 row vectors b and a, with coefficients in descending powers of z.