The engineering terminology for one use of Fourier transforms. By breaking up a wave pulse into its frequency spectrum
(1)

the entire signal can be written as a sum of contributions from each frequency,
(2)

If the signal is modified in some way, it will become
(3)
 
(4)
 
(5)
 
(6)

where is known as the "transfer function." Fourier transforming and ,
(7)

(8)

From the convolution theorem,
(9)
