0 , x < -1
I0(a sqrt(1 - x^2)
w(x) = ------------------ , -1 <= x <= 1
I0(a)
0 1 < x
This window sits on a pedestal of height 1/I0(a). The discrete-time window
of length N is obtained by setting x = 2n/(N-1)-1, for 0 <= n < N.
The parameter a (alpha) determines the shape of the window, with increasing a giving a larger mainlobe width. For a=0, the window is a rectangular. For a = 5.4414, the window has the same mainlobe width as a Hamming window.