Autocorrelation Explorer
Draw any signal in the top panel. The autocorrelation R(τ) appears in the middle — peaks reveal hidden periodicities. The bottom shows the power spectrum |F(ω)|² — the Wiener-Khinchin theorem says these two are Fourier transform pairs.
Signal x(t) — Draw here
Autocorrelation R(τ) = Σ x(t)·x(t+τ)
Power Spectrum |X(ω)|²
Wiener-Khinchin theorem: Power spectrum = FT of autocorrelation. Peaks in R(τ) correspond to peaks in |X(ω)|².