The Signal Processing Toolbox™ product provides a function, spectrogram, that returns the time-dependent Fourier transform for a sequence, or displays this information as a spectrogram. The time-dependent Fourier transform is the discrete-time Fourier transform for a sequence, computed using a sliding window. This form of the Fourier transform, also known as the short-time Fourier transform (STFT), has numerous applications in speech, sonar, and radar processing. The spectrogram of a sequence is the magnitude of the time-dependent Fourier transform versus time.
To display the spectrogram of a linear FM signal:
fs = 10000; t = 0:1/fs:2; x = vco(sawtooth(2*pi*t,.75),[0.1 0.4]*fs,fs); spectrogram(x,kaiser(256,5),220,512,fs,'yaxis')