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

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

[Jan]

Please format the code properly.

[Jennifer Miller]

Sorry this is the first time I have used the forum, I didn't realise you could do this.

[Star Strider]

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.

Answer 1

[Jan]

 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.

[Jennifer Miller]

Yes it is part of my path and the file has the.m extension. The file was set to open with a different software and by changing the preferred program for opening it to MATLAB the function will now run. However it appears that my output is not defined and the function is just producing "ans". I don't know how to define the output variables as I thought function[EMG_filtered] did this?

[Jan]

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]

Thank you for that helpful command. It returned only one version of the file and I checked that it has been saved