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How to obtain the frequency of a signal as function of the time?

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Giuseppe Naselli
Giuseppe Naselli on 10 Apr 2013
I have a discrete signal sampled at 0.005 seconds. (a 2-columns vector, the first colum is the time the second the value of the signal)
Plotting the signal as function of the time, it is possible to observe that
a) the signal amplitude decreases with time
b) the signal frequency increases with time
Therefore, I wish to plot two different things
1) the frequency of the signal as function of the time
2) the absolute value of the signal amplitude as function of the frequency
how can I do that? I will really appreciate if you can provide an example
Thanks in advance for your help !!!!!
G

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Answers (1)

Youssef  Khmou
Youssef Khmou on 10 Apr 2013
hi, This signal seems like a decreasing linear Chirp :
1) Frequency as function of time is called ' spectrogram') try :
doc spectrogram
S = spectrogram(x(:,2)) % because the second column contains the signal .
2) You can use the FFT function , many resources are available , try my submission : http://www.mathworks.com/matlabcentral/fileexchange/40002-psd-power-spectral-density-and-amplitude-spectrum-with-adjusted-fft

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