Fourier tutorials are a dime a dozen, so it would likely have been a better idea to link to his excellent wavelet tutorial at https://www.continuummechanics.org/wavelets.html . Good explanations of that concept are a lot harder to come by.
That is an excellent description of wavelets from one of the first points: "The vast majority of wavelet documents and internet tutorials appear to be written by mathematicians for mathematicians." all through the article.
