MATLAB: Time and Frequency analysis

fast fourier transformtime and frequency analysistime series

Hello,

I have data of measured signal in time. I want to know the frequencies of the components of my signal (Large scale fading+Small scale fading+Noise). For this reason, I have represented the FFT of my signal. I would like to know the time instant where the peaks highlited in yellow happened. Does any one have an idea how to do it?

Another question, How can I extract each component of the original signal from the FFT representation?

Thank you in advance.

Best Answer

The peaks in the fft result can occur anywhere in the signal. To do a time-frequency analysis, use the spectrogram function.

Related Solutions

MATLAB: How to convert the units of the y-axis into miliseconds^2/Hz in power spectral density analysis of an ECG signal

The y-axis on a PSD estimate will not be in units of the time squared, it will be in amplitude squared per Hz, so for an ECG signal I assume that will be in millivolts, not milliseconds. The recorded values of the waveform are not in time.

Since you are using dspdata.psd, why not just use spectrum.periodogram?

    psdest = psd(spectrum.periodogram,ecg,'NFFT',length(ecg),'Fs',fs);
    plot(psdest)

If you want to plot without using dB (that is preferred by the way)

   plot(psdest.Frequencies,psdest.Data)

MATLAB: Fft with frequency axis on log scale

Hi, You can just save the output of psd() and use semilogx

fs=2000; 
Hs=spectrum.periodogram; % Use default values 
psdest = psd(Hs,Signal,'Fs',fs);
semilogx(psdest.Frequencies,10*log10(psdest.Data));
grid on;

Best Answer

Related Solutions

MATLAB: How to convert the units of the y-axis into miliseconds^2/Hz in power spectral density analysis of an ECG signal

MATLAB: Fft with frequency axis on log scale

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