sentences:  A time-frequency representation describes the
  variation of spectral energy distribution over time, much as
  a musical score describes the variation of musical pitch
  over time.In audio signal analysis, the spectrogram is the most
  commonly used time-frequency representation, probably
  because it is well understood, and immune to so-called
  "cross-terms" that sometimes make other time-frequency
  representations difficult to interpret.But the windowing
  operation required in spectrogram computation introduces an unsavory tradeoff between time resolution and frequency
  resolution, so spectrograms provide a time-frequency
  representation that is blurred in time, in frequency, or in
  both dimensions.