Cycles-per-time spectral density
= Cycles-per-time spectral density
{title2=$f_c(\omega)=2\pi f_a(2\pi\omega)$}
In cycles per observation, frequency lies in $[-1/2,1/2]$ and $\gamma(h)=\int e^{2\pi ih\omega}f_c(\omega)\,d\omega$. Compared with angular-frequency density $f_a$, one has $f_c(\omega)=2\pi f_a(2\pi\omega)$. In particular, <white noise> of <variance> $\sigma^2$ has $f_c=\sigma^2$.