A method of modifying acoustic characteristics of an original audio signal as a function of modification instructions relating at least to the fundamental frequency and the spectral envelope of the original signal. The method comprises a first modification operation applied to the original signal to deliver an intermediate audio signal, the first modification operation being intended to deform the spectral envelope of the original signal in application of said spectral envelope modification instruction; and a second modification operation applied to the intermediate signal to deliver a final audio signal, the second modification operation being intended to modify at least the fundamental frequency of the intermediate signal, in application of a modification factor that is determined so as to take account of the effects of the first modification operation on the fundamental frequency of the original audio signal, so that the fundamental frequency obtained for the final signal conforms to said instruction relating to fundamental frequency.