General Form:

spec start_freq stop_freq step_freq vector [vector ...] 

Calculates a new complex vector containing the Fourier transform of the input vector (typically the linearized result of a transient analysis). The default behavior is to use a Hanning window, but this can be changed by setting the variables specwindow and specwindoworder appropriately.

Typical usage:

ngspice 13 -> linearize 
ngspice 14 -> set specwindow = "blackman" 
ngspice 15 -> spec 10 1000000 1000 v(out) 
ngspice 16 -> plot mag(v(out))

Possible values for specwindow are: none, hanning, cosine, rectangular, hamming, triangle, bartlet, blackman, gaussian and flattop. In the case of a Gaussian window specwindoworder is a number specifying its order. For a list of window functions see 17.5.27.