# Revista Matemática Iberoamericana

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**Volume 11, Issue 2, 1995, pp. 334–354**

**DOI: 10.4171/RMI/175**

Published online: 1995-08-31

Localisation fréquentielle des paquets d'ondelettes

Éric Séré^{[1]}(1) Université de Paris Dauphine, France

Orthonormal bases of wavelet packets constitute a powerful tool in signal compression. It has been proved by Coifman, Meyer and Wickerhauser that "many" wavelet packets $w_n$ suffer a lack of frequency localization. Using the $L^1$-norm of the Fourier transform $\hat{w}_n$ as localization criterion, they showed that the average $2^{–j} \sum^{2^j–1}_{n=0} \|\hat{w}_n\|_{L^1}$ blows up as $j$ goes to infinity. A natural problem is then to know which values of $n$ create this blowup in average. The present work gives an answer to this question thanks to sharp estimates on $\|\hat{w}_n\|_{L^1}$ which depend on the dyadic expansion of $n$ for several types of filters. Let us point out that the value of $\|\hat{w}_n\|_{L^1}$ is a weak localization criterion, which can only lead to a lower estimate on the variance of $\hat{w}_n$.

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Séré Éric: Localisation fréquentielle des paquets d'ondelettes. *Rev. Mat. Iberoam.* 11 (1995), 334-354. doi: 10.4171/RMI/175