∫ − ∞ ∞ ( ( | s ( t ) | ) 2 ) , d t {\displaystyle \int _{-\infty }^{\infty }\left((|s(t)|)^{2}\right),dt} in time transforms to ∫ − ∞ ∞ ( ( | S ( f ) | ) 2 ) , d f {\displaystyle \int _{-\infty }^{\infty }\left((|S(f)|)^{2}\right),df} in frequency
in time transforms to 
in frequency