sentences:  In
  the case of the spectrogram or the short-time Fourier transform, 
  the method of reassignment sharpens blurry
  time-frequency data by relocating the data according to
  local estimates of instantaneous frequency and group delay.This mapping to reassigned time-frequency coordinates is
  very precise for signals that are separable in time and
  frequency with respect to the analysis window.Many signals of interest have a distribution of energy that
  varies in time and frequency.