III. MATHEMATICAL BACKGROUND
The Short-Time Fourier Transform (STFT) is mainly a se-ries of segmented and overlapped FFTs that occur across the data stream. In the STFT, the individual FFTs from these mul-tiple segments are rendered as either a 3D surface plot (or a 2D contour plot). Both give a good indication of the time-frequency properties of the data series. The Fourier transform (a one-dimensional function) of the resulting signal is taken as the window is slid along the time axis, resulting in a two-dimensional representation of the signal. Mathematically, this is written as: