MATLAB: Plotting the frequency spectrum

fftfrequencyplotspectrum

Hi,
I am having trouble plotting the frequency spectrum of a sine wave. For this code, i expect the main frequency component to be centered around 1/(2*pi), but they are not. Is there something I am missing in my code?
x = [0:0.1:2*pi];
y = sin(x);
z = fft(y);
z = fftshift(z);
N = length(y);
f = [-N/2:N/2-1]/N;
plot(f,abs(z))

Best Answer

Please try:
   %%Time specifications:
   Fs = 100;                      % samples per second
   dt = 1/Fs;                     % seconds per sample
   StopTime = 1;                  % seconds
   t = (0:dt:StopTime-dt)';
   N = size(t,1);
   %%Sine wave:
   Fc = 12;                       % hertz


   x = cos(2*pi*Fc*t);
   %%Fourier Transform:
   X = fftshift(fft(x));
   %%Frequency specifications:
   dF = Fs/N;                      % hertz
   f = -Fs/2:dF:Fs/2-dF;           % hertz
   %%Plot the spectrum:
   figure;
   plot(f,abs(X)/N);
   xlabel('Frequency (in hertz)');
   title('Magnitude Response');
HTH.
Rick
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