Help me understand spectrograms

For Nyquist programming, the Hann (Hanning) window function is often a good choice, both for its characteristics and because it is easy to generate in Nyquist.

; wlen is the windowsize in seconds (local time)
(mult 0.5 (sum 1 (osc (hz-to-step (/ wlen)) wlen *sine-table* -90)))

http://en.wikipedia.org/wiki/Window_function#Hann_.28Hanning.29_window