How can I use a function file to filter noise from an EMG signal

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Jennifer Miller
Jennifer Miller 2015-6-23
评论： Star Strider 2015-6-23
I have written a script file which uses butterworth to filter my signal in the following way:
[b1,a1]=butter(5,[48/Fs*2, 52/Fs*2],'stop');
[b2,a2]=butter(5,300/Fs*2,'low');
[b3,a3]=butter(5,10/Fs*2,'high');
x = filter(b1,a1,EMG);
x1 = filter(b2,a2,x);
EMG_filtered = filter(b3,a3,x1);
This works well however as I have several different EMG signals to filter I would like to write a function which does this.
I am new to writing functions and as a first attempt tried the following:
function[EMG_filtered] = noise_removal(EMG)
Fs = 2000;
[b1,a1]=butter(5,[48/Fs*2, 52/Fs*2],'stop');
[b2,a2]=butter(5,300/Fs*2,'low');
[b3,a3]=butter(5,10/Fs*2,'high');
x = filter(b1,a1,EMG);
x1 = filter(b2,a2,x);
EMG_filtered = filter(b3,a3,x1);
This returned the error message: Undefined function 'noise_removal' for input arguments of type 'double'.
I can see the function saved in folder I am using so I dont think this is the issue.
I appreciate any help or advice
Thanks
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Jennifer Miller
Jennifer Miller 2015-6-23
Sorry this is the first time I have used the forum, I didn't realise you could do this.
Star Strider
Star Strider 2015-6-23
Suggestions:
You can combine the high-pass and low-pass filters into one band-pass design, saving steps in both the design and filtering.
Using the filtfilt function would prevent phase distortion that filter produces.

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回答（1 个）

Jan
Jan 2015-6-23
编辑：Jan 2015-6-23
I can see the function saved in folder I am using so I don't think this is the issue.
But can MATLAB see this function?
Is the folder, which contains the M-file, part of your path? Is the M-file called "noise_removal.m"?
See pathtool or addpath.
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Jan
Jan 2015-6-23
Matlab does not care about the file association of the operating system. Therefore you must have changed something else and repaired it by accident.
If the variable EMG_filtered is created inside the code, it is replied to the caller also. Either you call another version of your M-file or you did not save the file after editing. Please check:
which noise_removal -all
Jennifer Miller
Jennifer Miller 2015-6-23
Thank you for that helpful command. It returned only one version of the file and I checked that it has been saved

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