MATLAB: Can I use FFT to determine the variable frequency

fft

Hi All.
Can I use Fourier transform to determine the variable frequency?Below is the code. If the frequency perturbation(rand/10) is small,the main frequency array(xx) contains the same value. If the frequency perturbeation(rand/10) is large, such as rand,the value in main frequency array(xx) does NOT make sense.
Is there any way I can find the variable frequency?
I appreciate any of your advice.
Ivy
clear all;
clc;
Fs=1000; 
T=1/Fs;
L=1000;
t=(0:L-1)*T;
for i=1:1:10000          %variable frquency signal.  
x(i)=0.7*sin(2*pi*(50+rand/10)*T*(i-1));  
end
for k=1:1:5000
NFFT =1024;
Y=fft(x(k:1024+k),NFFT);
f= 100*linspace(0,1,100);
[C,index]=max(abs(Y(1:100)));
xx(k)=f(index);
end

Best Answer

You may want to try the spectrogram function. For more information:
   >> doc spectrogram
HTH.
Rick
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