Introduction - If you have any usage issues, please Google them yourself
An immediate observation for those who deal with the processing of signals is the
omnipresence of the concepts of frequency, which are called “spectra” here. This
presence is important in the fields of theoretical research as well as in most applied
sectors of engineering. We can, with good reason, wonder on the pertinence of the
importance given to spectral approaches. On the fundamental plane, they relate to
the Fourier transformation, projection of signals, signal descriptors, on the basis of
special periodic functions, which include complex exponential functions. By
generalizing this concept, the basis of functions can be wider (Hadamard, Walsh, etc.),
while maintaining the essential characteristics of the Fourier basis. By projections, the
spectral representations measure the “similarity” between the projected quantity and a
particular base: they have henceforth no more – and no less – legitimacy than this.
Spectral_Analysis_Parametric_and_Non_Parametric_Digital_Methods_Digital_Signal_Image_Processing.pdf