FFT-Based Time-Frequency Analysis :: Special Topics (Signal Processing Toolbox)

Signal Processing Toolbox

FFT-Based Time-Frequency Analysis

The Signal Processing Toolbox provides a function, spectrogram, that returns the time-dependent Fourier transform for a sequence, or displays this information as a spectrogram. The Toolbox also inclues a spectrogram demo. 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')

Note that the spectrogram display is an image, not a plot.

Inverse Complex Cepstrum Median Filtering