How to integrate filter function into matlab code

Hello,

I am trying to batch process a bunch of EMG files using a matlab code. Part of the processing is to filter all EMG data using a 6th order butterworth bandpass filter from 30 to 300 Hz. I used filterBuilder and created a variable 'Hbp' to process my first file. So in my code i just had:

RPbandpass=filter(Hbp,RP_ROI);

I clear the workspace after each file so i can no longer just reference Hbp without going through filter builder again. I looked into the code generation options of filterBuidlder where i can generate a function that returns filter as output or generate fuction that filters my data. Both of those gave me some code but i'm not sure how exactly to implement that into my main code file. I am guessing that i want to have a bandpassfilter function saved and stored in my matlab directory that my code can reference but not sure how to do that. Any other solutions or tips are welcome and thank you for your help in advance!

Answer 1

[Bora Eryilmaz]

You can create the Butterworth filter directly and use it in your code without needing to store anything:

Fs = 2000; % Sampling rate 2000 Hz
bandPassRange = [30 300]; % in Hz.

% Note that the filter order will be 2 * 3.
[b,a] = butter(3, bandPassRange / (Fs/2), 'bandpass')

b = 1×7

0.0383 0 -0.1149 0 0.1149 0 -0.0383

a = 1×7

1.0000 -4.1361 7.2416 -6.9952 3.9888 -1.2706 0.1717

freqz(b,a,[],Fs)

You can learn more about it here: https://www.mathworks.com/help/signal/ref/butter.html

[Ines Shekhovtsov]

Thank you so much!

[Ines Shekhovtsov]

Just out of curiousity, how could i save the filterBuilder designed filter as a function and then use that in my code? I got this from the code generator inside filterBuilder:

function Hd = getFilter

%GETFILTER Returns a discrete-time filter object.

% MATLAB Code

% Generated by MATLAB(R) 9.12 and DSP System Toolbox 9.14.

% Generated on: 13-Dec-2022 11:11:53

N = 6; % Order

F3dB1 = 30; % First

F3dB2 = 300; % Second

Fs = 2000; % Sampling Frequency

h = fdesign.bandpass('n,f3db1,f3db2', N, F3dB1, F3dB2, Fs);

Hd = design(h, 'butter', ...

'SOSScaleNorm', 'Linf');

I know it's not this, but how would i call this filter in my code??

RPbandpass=filter(Hd,RP_ROI);

Thank you!

[Bora Eryilmaz]

Save the above code as a MATLAB script into an M file and run it again next time you need it.

Alternatively, you can save the Hd object into a MAT file as a variable using the save command.

[Ines Shekhovtsov]

Thank you. That's fairly simple!