Let denote the CrossCorrelation of functions and . Then
where denotes the Fourier Transform and

(2) 

(3) 
Applying a Fourier Transform on each side gives the crosscorrelation
theorem,

(4) 
If , then the crosscorrelation theorem reduces to the WienerKhintchine Theorem.
See also Fourier Transform, WienerKhintchine Theorem
© 19969 Eric W. Weisstein
19990525