How to Determine the Cutoff Frequency of Butterworth Low-Pass Filter When Filtering an EMG Signal ?

How to Determine the Cutoff Frequency of Butterworth Low-Pass Filter When Filtering an EMG Signal ?

I have an EMG Signal,and I want to use Butterworth Low-pass Filter of it;

The Matlab code for Butterworth Filter is :

[b,a] = butter (Order,Cutoff Freq/(sampling Freq/2),'Filter type');

b,a : Outputs

butter ; Buterworth Filter command

Order ; for first order write (1),Second order write (2) ...etc

Cutoff Freq ; cutoff frequency

Sampiling Freq ; Sampiling Frequency

Filter Type : Low-Pass Filter (low) High-Pass Filter (high)

[b,a] = butter (Order,Cutoff Freq/(sampling Freq/2),'Filter type');

is there a method or code to calculate Cutoff Frequency rather than trail and erorr ?

Answer 1

[Star Strider]

Use the fft or pspectrum functions to calculate the Fourier transform of the EMG data. Use that result to define the frequencies of interest and whatever could be considered ‘noise’, and then design the filter (usually lowpass or bandpass) to pass the desired frequencies and eliminate the noise. Also, while I have nothing against Butterworth filters, in general elliptic filters are more computationally efficient. (See: ellipord, ellip, zp2sos and filtfilt for details and other necessary information.)