define frequency of signal from fft output
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Ngoc Lam
el 29 de Sept. de 2014
Comentada: YAMASANI MANOJ REDDY
el 21 de Ag. de 2018
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/145546/image.png)
what is the relationship between the sampling frequency Fs and frequency of signal of FFT function in matlab? assUme that, we have a signal with spectrum as follow picture. with Fs= 44.1Khz, I know that X-axis is not the frequecy of signal, right? How to define the frequency of this signal with followed spectrum? for example, at the point X-axis = 10000, with Fs= 44.1Khz, how to define frequency of signal at that point?
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Rick Rosson
el 29 de Sept. de 2014
Editada: Rick Rosson
el 29 de Sept. de 2014
dF = Fs/N;
f = dF*(0:N-1)';
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Ngoc Lam
el 30 de Sept. de 2014
Editada: Ngoc Lam
el 30 de Sept. de 2014
1 comentario
Rick Rosson
el 30 de Sept. de 2014
The sampling rate in your code is
Fs = 500/(4*pi);
which is approximately 40 samples per second. By the Nyquist Sampling Theorem, the maximum frequency that you can represent without aliasing is Fs/2 or approx 20 Hertz. Your signal, however, contains components at 50 Hertz and 100 Hertz, which are well above the maximum.
Rick Rosson
el 30 de Sept. de 2014
Please try:
Fs = 1000;
dt = 1/Fs;
N = 12000;
t = dt*(0:N-1)';
x = sin(100*pi*t) + 2*cos(200*pi*t);
X = fftshift(fft(x))/N;
dF = Fs/N;
f = -Fs/2:dF:Fs/2-dF;
plot(f,abs(X));
1 comentario
Syed Masoud Shah kakakhel
el 23 de Mzo. de 2017
Editada: Syed Masoud Shah kakakhel
el 23 de Mzo. de 2017
kindly @Rick Rosson can u comment...variables like what is N?? kindly will be more helpful..m waiting for response
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