The present code is a Matlab program for Time-Frequency analysis of a given (non-stationary) signal. The results are:
1) graphical representation of the signal in the time domain;
2) graphical representation of the signal in the frequency domain (via FFT);
3) graphical representation of the signal in the time-frequency domain (via STFT).
The code is based on the theory described in:
 G. Heinzel, A. Rudiger, R. Schilling. Spectrum and spectral density estimation by the Discrete Fourier transform (DFT), including a comprehensive list of window functions and some new flat-top windows. Germany, Hannover, Max-Planck-Institut für Gravitationsphysik, 2002.
Hristo Zhivomirov (2020). Time-Frequency Analysis of Signals with Matlab (https://www.mathworks.com/matlabcentral/fileexchange/45465-time-frequency-analysis-of-signals-with-matlab), MATLAB Central File Exchange. Retrieved .
The magnitude of the frequency (and time-frequency) spectrum is given in dBV. The negative sign means that the actual (peak) level of the spectral lines is bellow 1 V. This is the most common case in the time-frequency and spectral analysis.
Hello sir, may I know why does your magnitude tend to negative.
@CUMT CHINA Good
[p,f,t] = pspectrum(y,Fs,'spectrogram','TimeResolution',400/fs);instfreq(p,f,t)
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Thank you for every good work you have done!
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