Spectral Flux
A feature extractor that extracts the Spectral Flux from a window of samples and
the preceeding window. This is a good measure of the amount of spectral chagne
of a signal.
Spectral flux is calculated by first calculating the difference between
the current value of each magnitude spectrum bin in the current window from
the corresponding value of the magnitude spectrum of the previous window.
Each of these differences is then squared, and the result is the sum of the
squares.
