How can i susstract a gamma wavelenght from a eeg signal ??

This is my code and i need to sustract either of the 5 types of waves theta, gamma, delta, beta %Procesare semnal EEG - 8 canale %Am ales un singur canal % =xlsread('C:\Users\Hell\Desktop\pptrm\tema2rm'); y1= xlsread('C:\Users\Hell\Desktop\pptrm\tema2rm\dap.xls'); y1 = y1(:,2); fs = 500;% Frecventa de esantionare (Hz) N = length(y1); T = 1/fs; % T reprezinta perioada de esantionare in secunde ls = size(y1); %% marime fs2 = 1/ N;% gasirea frecventei t = (0 : N-1) /fs; %timpul t1 = (0 : N-1) *T;%t = (0:1:length(y1)-1)/fs; % perioada de esantionare Nyquist = fs/2; %criteriul Nyquist figure; plot(t,y1,'b'); title ('Semnal EEG intr-o criza epileptica') xlabel ('time (sec)') ylabel ('Amplitute (uv)') grid on; figure; y1inainte = y1(5:400); N1 = length(y1inainte);%nr esantioane tinainte = (0 : N1-1) /fs; subplot (3,1,1); plot(tinainte,y1inainte,'b'); title ('Semnal EEG inainte de criza epileptica') xlabel ('time (sec)') ylabel ('Amplitute (uv)') grid on; y1intimp = y1(800:1100); N2 = length(y1intimp);% nr esantioane tintimp = (0 : N2-1) /fs; %figure; subplot (3,1,2); plot(tintimp,y1intimp,'b'); title ('Semnal in timpul crizei epileptice ') xlabel ('time (sec)') ylabel ('Amplitute (uv)') grid on;

y1dupa = y1(1100:1600 ); N3 = length(y1dupa); tdupa = (0 : N3-1) /fs; %figure; subplot (3,1,3); plot(tdupa, y1dupa,'b'); title ('Semnal dupa criza epileptica ') xlabel ('time (sec)') ylabel ('Amplitute (uv)') grid on;

%%Transformata Fourier:
%%se calculeaza TFD cu FFT
 X = fftshift(fft(y1));% se deplaseaza spectru pentru a avea originea la mijlocul reprezentarii
 X1= fftshift(fft(y1inainte));
 X2= fftshift(fft(y1intimp));
 X3= fftshift(fft(y1dupa));
 %%Specificatii frecvente:
 dF = fs/N;                      % Hz
 f = -fs/2:dF:fs/2-dF;           % Hz
  %%Specificatii frecvente:
 dF1 = fs/N1;                      % Hz
 f1 = -fs/2:dF1:fs/2-dF1;           % Hz
  %%Specificatii frecvente:
 dF2 = fs/N2;                      % Hz
 f2 = -fs/2:dF2:fs/2-dF2;           % Hz
  %%Specificatii frecvente:
 dF3 = fs/N3;                      % Hz
 f3 = -fs/2:dF3:fs/2-dF3;           % Hz
 %%Plot spectru:
 figure;
 subplot (2,2,1);
 plot(f,abs(X)/N);
 xlabel('Frectventa (Hz)');
 title('Magnitudinea rasp. original');
  %%Plot spectru: Inainte de crize epileptice
 %figure;
 subplot (2,2,2);
 plot(f1,abs(X1)/N1);
 xlabel('Frecventa (Hz)');
 title('Magnitudinea rasp inainte de crize');
   %%Plot spectru: In timpul crizelor epileptice
 %figure;
    subplot (2,2,3);
 plot(f2,abs(X2)/N2);
 xlabel('Frecventa (Hz)');
 title('Magnitudinea rasp in timpul crizelor');
   %%Plot spectru: Dupa crizele epileptice
 %figure;
    subplot (2,2,4);
 plot(f3,abs(X3)/N3);
 xlabel('Frecventa (Hz)');
 title('Magnitudinea rasp.dupa crize epileptice');
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
ff=[0  0.1 0.11 0.15 0.16 1]; %filtru trece banda
af=[ 0 0 1 1 0 0 ];  
nf=100; % dimensiunea filtrului 
b=firpm(nf, ff, af); % coeficientii filtrului 
ytb=filter(b,1,X); % iesirea filtrului

figure subplot(2,1,1); plot_t(T,ytb); subplot(2,1,2); plot_S(T,ytb);

Answer 1

[Sameer]

Hi @Elena Alexandra Gradescu

To remove one of the main EEG wave types (like theta, gamma, delta, or beta) from your signal, you can use a band-stop filter for that frequency range.

For example, to remove the theta band (4–8 Hz):

fs = 500; % Sampling frequency (Hz)
order = 100; % Filter order

% Theta band (4-8 Hz) normalized
theta_low = 4 / (fs/2);
theta_high = 8 / (fs/2);

% Design band-stop filter
b = fir1(order, [theta_low theta_high], 'stop');

% Filter the EEG signal
y1_no_theta = filtfilt(b, 1, y1);

% Plot result
plot(y1_no_theta);
title('EEG after Theta (4-8 Hz) Removal');

Change the frequency range for delta, beta, or gamma as needed.

• Delta: 0.5–4 Hz
• Beta: 13–30 Hz
• Gamma: 30–100 Hz

This will subtract (remove) the chosen frequency band from your EEG signal.

Hope this helps!