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Fig. 10. A few milliseconds from vowel [ae] “had,” comparing the visibility of reso- nance components in a conventional spectrogram (upper) against a reassigned spectrogram plotted using Nelson’s component isolation technique. Both are com- puted using 5.9 ms analysis frames.
work—have each recognized that, for many applications, it is the components of a signal that contain the most sought information, not the overall energy distribution. Going hand in hand with this break from tradition, by focusing entirely on instantaneous frequencies the method sets aside the “clas- sical” Fourier spectrum which decomposes a signal (or its successive frames, in the spectrogram) into sine waves of infinite extent. From the perspective of signal modeling, we already know that real signals are never so constituted, so it is not exactly a leap of faith to stop representing them that way. It is our hope that the future will bring production-qual- ity software that everyone can access, which allows a choice between conventional and reassigned spectrograms. For many applied acousticians, the choice will be clear.AT
References for further reading:
32 Acoustics Today, July 2006