2. Wavelets and wavelet packets

2.1 Reminders about wavelets

The advantage of Fourier analysis, widely used to study the spectral components of a phenomenon, is that it can describe a system in terms of its frequency rather than time characteristics, thus complementing the classical representation. However, a poor description in either representation can lead to a poor overall understanding of a phenomenon. The ideal representation is the one that gives the best possible description for a given system. To achieve this, it is necessary to use a method that can simultaneously perform an analysis with time and frequency parameters, like a musical score where the frequency and duration of the notes are indicated. In this section, we present a few examples of time-frequency analyses, all of which share the principle...