A new trial for determining an optimal order of expansion terms for the state probability distribution is proposed. Furthermore, part of the effectiveness of the proposed method is experimentally confirmed by applying it to data actually observed in the sound environment.On propose un nouveau type de banc d'essai pour determiner l'ordre optimal de developpement de la distribution des etats de probabilite. L'efficacite de la methode proposee est confirmee experimentalement en l'appliquant aux donnees observees dans un environnement sonore.