Some traditional digital signal processing techniques encompass enhancement, filtering, coding, compression, detection and recognition. Recently, it has been presented a new hypothesis of signal processing known as the ability of adaptation of speech signals: an original speech signal may sound similar to a target speech signal if a relocation process of its wavelet coefficients is applied. This hypothesis is true under some conditions theoretically defined. In this paper we present the basic idea behind the hypothesis of adaptation and moreover, we test the hypothesis within four cases: speech signals with the same gender and language, speech signals with the same gender but different language, speech signals with the same language but different gender, and speech signals with different gender and language. It is found that the hypothesis is true if the requirements are satisfied, even if the gender or the language of the original and target signals are not the same.