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

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Elena Alexandra Gradescu
回答： Sameer 2025-5-16
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);

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回答（1 个）

Sameer
Sameer 2025-5-16
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!

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