Friedman's instantaneous frequency density A first example is the instantaneous frequency density : so as to take advantage of the phase structure of the short-time Fourier transform (STFT), Friedman simply computed at each time $t$ the histogram of the frequency displacements $\hat{\nu}(x;t,\nu)$ of the spectrogram. The resulting time-frequency representation is no more an energy distribution, and could be derived as well from any other reassigned distribution. Here is an example of this instantaneous frequency density, obtained with the M-file friedman.m on the pseudo-WVD of the previous signal (see fig. 4.38): >> t=1:2:127; [tfr,rtfr,hat]=tfrrpwv(sig,t); >> friedman(tfr,hat,t,'tfrrsp',1); Figure: Instantaneous frequency density defined by Friedman, computed from the frequency displacements $\hat{\nu}(x;t,\nu)$ of the pseudo-WVD Although some cross terms are still present, the localization of the components is quite good, especially for the chirp components.
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