In this paper, we present a new design of a psychoacoustic model following the example model used in audio standard MPEG-1 layer 3 with the gammachirp wavelet packet decomposition. The essential characteristic of this model is that it proposes an analysis by wavelet packet transformation on the frequency bands that come closer the critical bands of the ear that differs from the existing model based on an analysis by a short-term Fourier transformation. 1