Understanding Acoustic Emission Testing- Reading 1 Part B-A

Fourier-Transform (FT) of Frequency
To understand any complicated signal, one of the first step is to generate the Fourier
transform of that signal. Fourier transform is a mathematical function that decomposes
a time varying signal, as shown in figure to the right, into several sinusoidal waves.
These sinusoidal waves will have different frequency, amplitude and phases but when
you add them all together, the original waveform is magically recreated. The
fundamental idea here is complexity reduction by splitting a waveform into
manageable chunks. For reasons that initially baffled me, the powers there be chose
sinusoidal waves as this manageable chunk.
Charlie Chong/ Fion Zhang
https://ranabasheer.wordpress.com/2014/03/16/why-do-we-use-fourier-transform/