Hello,
I doesn't understand the amplitude given by the FFT function. Indeed I use it to calculate the DFT of a sum of sine and the amplitude returned is divided by 2 wrt the amplitude of my original function. The frequencies are correct
Does anyone can explain it to me ?
Please find hereunder the code I used :
T = 0:0.01:10;T = T';x1 = 0.5*sin(2*pi*2*T);x2 = 1.2*sin(2*pi*5.4*T);x3 = 0.7*sin(2*pi*7*T);y = x1+x2+x3;N = length(y);duree = max(T)-min(T);Delta_T = duree/N;Fe = N/duree;Delta_F = 1/duree;xfft = 1/N*fft(y);mag = abs(xfft);freq = 0:Delta_F:(Fe-Delta_F);freq = freq';figure(2)hold all;plot(freq,mag);legend('abs');xlabel('Freq in Hz');title('FFT');box on;set(gca,'Xlim',[0 100]);grid on;figure(1)hold all;plot(T,y)grid on
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