Evolution temporelle de la variabilité du spectre moyen à long terme

Abstract
Most research concerning the Long Term Average Spectrum (LTAS) variability has consisted in analyses of contemporary vocal utterances but others studies have nevertheless revealed the presence in LTAS of a specific variability depending on time. Furui et al ( [ l ], [2] ) have shown a good Long Term Cepstrum stability for periods that do not exceed 3 weeks but a significant variability is progressively detected for longer periods. This communication must be inserted in the research work aiming at systematization of all the studies centered on the comparisons of recordings collected at 5-year intervals in similar experimental conditions.