Hi Julian,
It is my understanding that you are looking to perform a time-frequency analysis on signals where the frequency content changes over time. 'FFT' is a powerful tool for analyzing the frequency content of signals but is limited, as it assumes the frequency content is stationary.
For non-stationary signals, 'Short-Time Fourier Transform (STFT)' may be more appropriate. 'STFT' divides the signal into small enough segments where the signal's frequency content is assumed to be stationary. This method allows you to see how the frequency content of your signal changes over time. You could use 'spectrogram' function in MATLAB to perform 'STFT'. This function will give you a time-varying frequency spectrum of your signal.
The following code snippet provides a rough implementation:
Fs = 1000; % Sampling frequency
T = 1/Fs; % Sampling period
L = 1000; % Length of signal
t = (0:L-1)*T; % Time vector
% Create a non-stationary signal
v = sin(2*pi*t.^2);
% Perform STFT
window = 256; % Window length for STFT
noverlap = 250; % Number of overlapping samples
nfft = 1024; % Number of FFT points
[s,f,t,p] = spectrogram(v,window,noverlap,nfft,Fs,'yaxis');
% Plot the spectrogram
surf(t,f,10*log10(abs(p)),'EdgeColor','none');
axis xy; axis tight; colormap(jet); view(0,90);
xlabel('Time (s)');
ylabel('Frequency (Hz)');
title('Spectrogram');
Kindly have a look at the following documentation links to have more information on:
- 'spectrogram' function: https://www.mathworks.com/help/signal/ref/spectrogram.html
- 'surf' function: https://www.mathworks.com/help/matlab/ref/surf.html
Hope that helps!
Balavignesh
