How to find out roll-off from magnitude response of filter in matlab

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632541 2021-9-23

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https://ww2.mathworks.cn/matlabcentral/answers/1459079-how-to-find-out-roll-off-from-magnitude-response-of-filter-in-matlab

评论： 632541 2021-9-23

How to find out roll-off from magnitude response of filter in matlab?

This is from doc frequency response of matlab site

https://in.mathworks.com/help/signal/ug/frequency-response.html

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Chunru 2021-9-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1459079-how-to-find-out-roll-off-from-magnitude-response-of-filter-in-matlab#answer_793414

在 MATLAB Online 中打开

fs = 2000;

[b,a] = butter(9,400/(fs/2));

[h, f] = freqz(b,a,16384,fs);

h = 20*log10(abs(h));

[~, i3db] = min(abs(h - 10*log10(1/2)));

f3db = f(i3db);

plot(f, h);

xline(f3db)

grid on

ylim([-60 0])

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Chunru 2021-9-23

Shouldn't you come out your design first?

632541 2021-9-23

在 MATLAB Online 中打开

Please have a look at it

fs= 50e3;      
cutOff= 5;       
order = 3;
t=0:1/fs:1-(1/fs);
Sig=sin(2*pi*200*t)+sin(2*pi*150*t);
noise=2*rand(size(t))+sin(2*pi*1*t)+sin(2*pi*5*t)+sin(2*pi*3*t)+sin(2*pi*7*t)+sin(2*pi*11*t)+sin(2*pi*0.5*t)+sin(2*pi*0.2*t);
noisySig = Sig+noise;
wn= 2*cutOff/fs;
[B, A] = butter(order,wn,'high');                        
freqz(B,A);                                       %%Freq response of filter
filteredData=filtfilt(B,A,noisySig); 