Hidden Markov tree based transient estimation for audio coding

A new approach for transients detection and estimation in the context of hybrid audio coding is presented. The basic idea is to use an orthogonal dyadic wavelet expansion, followed by hidden Markov tree modeling of wavelet coefficients. Coefficients may be cast as "transient type" or "residual type", and the estimated transient is reconstructed from the transient type coefficients only. The estimation procedure involves the classical two steps of hidden Markov models: parameters estimation and state estimation. The implementation of those two steps in the case of wavelet coefficient trees is discussed in some detail, and numerical results are given. The application to audio signal encoding is also discussed.