Computes the spectral flux feature of the current frame
    ARGUMENTS:
        X:            the abs(fft) of the current frame
        X_prev:        the abs(fft) of the previous frame

def stSpectralFlux(X, X_prev):
    """
    Computes the spectral flux feature of the current frame
    ARGUMENTS:
        X:            the abs(fft) of the current frame
        X_prev:        the abs(fft) of the previous frame
    """
    # compute the spectral flux as the sum of square distances:
    sumX = numpy.sum(X + eps)
    sumPrevX = numpy.sum(X_prev + eps)
    F = numpy.sum((X / sumX - X_prev/sumPrevX) ** 2)

    return F