A method and apparatus are provided for evaluating a quality, as perceived by a recipient, of a signal carrying a stimulus. The method includes a step for detecting absences of variation of said signal and a step of quantifying at least one deterioration corresponding to an absence of variation. The quantity of deterioration computed during the quantification step depends on an amplitude of variation of the stimulus immediately following the concerned absence of variation. The method and apparatus enable the correlation of the duration of variance, possible past of invariances and a sudden variation of amplitude following said in variance, in implementing an automatic technique in real time, for example.