fft of a 2 simple cos functions
2 views (last 30 days)
Show older comments
Hi Folks,
I need to modify the code so that I am reporting the correct frequencies calculated from the fft
Fs=9827.2*2;
t=0:1/Fs:0.06756;
f=14.8;
f_1=1228.4;
x=cos(2*pi*t*f)+cos(2*pi*t*f_1);
nfft=664;
X=fft(x,nfft);
X = X(1:nfft/2);
mx=abs(X);
f=(0:nfft/2-1)*Fs/nfft/2;
figure(1);
plot(t,x);
title('Cosine wave Signal');
ylabel('Amplitude');
figure(2);
plot(f,mx);
title('Power Spectrum of a sine wave');
xlabel('Frequency(hz)');
ylabel('Power')
I expect to see the 2 fundamental frequencies 14.8Hz and 1228.4Hz (83*14.8) in the frequency window, however, it reports 14.8Hz and 621.9Hz( 14.8*42)instead.
Thanks
0 Comments
Accepted Answer
Rick Rosson
on 9 Jan 2015
Replace the following line:
f=(0:nfft/2-1)*Fs/nfft/2;
with:
f=(0:nfft/2-1)*Fs/nfft;
0 Comments
More Answers (0)
See Also
Categories
Find more on Fourier Analysis and Filtering in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!