numerator and denominator coefficients from designfilt function

Question

Rohit Mallampati 2020-7-13

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/564182-numerator-and-denominator-coefficients-from-designfilt-function

回答： Peter Bode 2021-3-1

I am designing an lowpass IIR filter using designfilt function. I found coefficients for the filter which is 9x6 Double. Now, how can I find numerator and denominator from this?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Nipun Katyal 2020-7-15

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/564182-numerator-and-denominator-coefficients-from-designfilt-function#answer_466094

在 MATLAB Online 中打开

The type of coefficients you encounter are called Second order section coefficients. Second-order section coefficients, specified as a matrix. sos is a K-by-6 matrix, where the number of sections, K, must be greater than or equal to 2. If the number of sections is less than 2, the function treats the input as a numerator vector. Each row of sos corresponds to the coefficients of a second-order (biquad) filter. The ith row of sos corresponds to [bi(1) bi(2) bi(3) ai(1) ai(2) ai(3)].

%Create a filter object using designfilt
filterObj = designfilt('lowpassiir', 'PassbandFrequency', .45, 'StopbandFrequency', .55, 'PassbandRipple', 1, 'StopbandAttenuation', 60);
%Convert the second order section coefficients to tranfer function format
[b,a] = sos2tf(filterObj.Coefficients);
%Here b is the numerator and a is the denominator

2 个评论
显示无隐藏无

Rohit Mallampati 2020-7-15

Thanks Nipun

John Gauci 2021-2-1

在 MATLAB Online 中打开

This does not always work. For example:

filterObj2 = designfilt('lowpassiir', 'PassbandFrequency', 0.02, 'StopbandFrequency', 0.04, 'PassbandRipple', 1, 'StopbandAttenuation', 60);
fvtool(filterObj2);
[b,a] = sos2tf(filterObj2.Coefficients);
fvtool(b,a);