I have a raw eeg data and i want to plot the alpha wave(8-12Hz) of this data in the same window . How can i do? please help me

Here is some prototype code. I will let you adapt it to your needs, rather than do all of it for you. See the documentation on ellipord, ellip, zp2sos ,freqz and filtfilt for those details.

Fs = ...;                                                   % Sampling Frequency
Fn = Fs/2;                                                  % Nyquist Frequency
Wp = [8 12]/Fn;                                             % Normalised Passband Frequencies
Ws = Wp.*[0.98 1.02];                                       % Stopband Frequencies
Rp =  1;                                                    % Passband Ripple/Attenuation
Rs = 60;                                                    % Stopband Ripple/Attenuation
[n,Wn] = ellipord(Wp,Ws,Rp,Rs);                             % Calculate Filter Order
[z,p,k] = ellip(n,Rp,Rs,Wp);                                % Design Filter
[sos,g] = zp2sos(z,p,k);                                    % Implement Filter As Second-Order-Section Representation
figure
freqz(sos, 2^16, Fs)                                        % Filter Bode Plot
% set(subplot(2,1,1), 'XLim',[0 15])                          % Optional
% set(subplot(2,1,2), 'XLim',[0 15])                          % Optional
EEGfilt = filtfilt(sos,g,EEG);                              % Filter EEG

This assumes the the original signal is ‘EEG’. The freqz call allows you to be sure that the filter does what you want it to. If it does not, change the filter design until it does. It is also possible to specify ‘Ws’ as specific frequencies, similar to the way I specified ‘Wp’ here.

Another option is to use the designfilt function (introduced in R2014a), and it has a few more options. I simply prefer to use command-line functions.

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vo 2022-12-15

hi @Star Strider Can you help me one more?

I wonder if I use function bandpass, Do I need a step denoise a signal before, or not?

Star Strider 2022-12-15

I do not understand ‘step denoise a signal’. I would just filter the signal with the bandpass function. There is no specific need to do any other processing on it before filtering it. If you want to do further processing on it afterwards, then it is appropriate to do that on the filtered signal. One such approach could be to remove broadband noise (that no frequency selective filter is capable of completely removing). I do not have your EEG signals, so I cannot determine if that is necessary. (The easiest approach to that problem would be to use the sgolayfilt function.)

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