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FFT EXECUTION ON EEG SIGNAL using MATLAB

I purchased a 5-minute raw eeg from NEXUS 10 mark 2 equipment and it gives me 1 x 76800 lines of output to Matlab. as I understand it, the sampling frequency is chosen to be 256 Hz, so it gives me a total of 76800 sampling points. no wat i m perfecting N-point FFT on this raw eeg signal. since N can only be degree 2 I EXPRESSING 65536 (2 ^ 16) REPORTS FROM PRODUCTION FROM RAW EGG, i.e. out of 76800 points, I took 65536. Now I can’t do fft on this vector (65536 sample points) please, can anyone direct .. and I'm new ... I tried so far

       x=raw(1,1:65536); %raw eeg contain 76800 points , 65536 points are taken 
                         from this
       N=length(x);
       fs=256;
        ts=1/fs;
        tmax=(N-1)*ts;
        t=0:ts:tmax;
        plot(t,x);  % plot time domain

        f=-fs/2:fs/(N-1):fs/2;
        fftval=fft(x);                                                              
        plot(f,ffval); % plot freq domain

, . stackoverflow, . , . , POSTS.PLEASE HELP

+1
2

, :

load('eeg_4m.mat')
fs=2048;
x=val(1,:);
N=length(x);
ts=1/fs;
tmax=(N-1)*ts;
t=0:ts:tmax;
plot(t,x);  % plot time domain

nfft = 2^( nextpow2(length(x)) );
df = fs/nfft;
f = 0:df:fs/2;
X = fft(x,nfft);
X = X(1:nfft/2+1);
figure; plot(f,abs(X)); axis([0,50,0,10e6]); % plot freq domain
0

768000 - FFT. : 2 ^ 11 * 3 * 5 ^ 3

15 .

, 2. .

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