butterworth filter

Question

Sam Hamie 2012-3-19

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https://ww2.mathworks.cn/matlabcentral/answers/32758-butterworth-filter

I made the simple code for butterworth but i keep getting this error! Butter is not defined! can someone help?

>> order =1; >> sampling_freq=1000; >> cut_off_freq=10; >> [butter_b,butter_a]=butter(order, cut_off_freq/(sampling_freq)/2); ??? Undefined function or method 'butter' for input arguments of type 'double'.

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Honglei Chen 2012-3-19

Please don't post the same question twice. If necessary, you can always update your original question. I've answered this in your original thread

http://www.mathworks.com/matlabcentral/answers/32748-butterworth-filter

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Answer 1

Wayne King 2012-3-19

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在 MATLAB Online 中打开

Hi Sam, do you have the Signal Processing Toolbox installed?

if you enter

>>ver

do you see an entry for Signal Processing Toolbox?

If you enter:

license('test','signal_toolbox')

Do you get a 1?

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Sam Hamie 2012-3-20

Hello Wayne

Actually I dont have signal processing toolbox installed. and my >> license('test','signal_toolbox')

ans = 0

Please let me know where to get the signal processing toolbox?

I appreciate your help.

Thanks

sam

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Answer 2

Wayne King 2012-3-20

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https://ww2.mathworks.cn/matlabcentral/answers/32758-butterworth-filter#answer_41392

Hi Sam, You must contact MathWorks for licensing a new toolbox in your installation. And please do follow Honglei's good advice about double posting.

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Sam Hamie 2012-3-20

hello wayne,

is there a way were I can use any filter to clean/smooth my graph? My graph is only a bunch of data on X & Y axis!

It has to be a way were I can bypass the Signal Processing Toolbox!

thanks,

sam

Honglei Chen 2012-3-20

If you just want to smooth the data, you can do a moving average, e.g., h = 0.25*ones(4,1) produces a 4-points moving average filter and you can filter your data x using conv(h,x).

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Answer 3

Daniel Shub 2012-3-20

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https://ww2.mathworks.cn/matlabcentral/answers/32758-butterworth-filter#answer_41395

Depending on how many filters you need and their orders, you may be able to calculate the coefficients by hand. You will probably need the signal processing toolbox to do anything useful with the coefficients...