Catalan has been studied by several authors, who gave phonologic as well as phonetic descriptions of the language. In most studies, authors have nevertheless focussed on categories of sounds, considered each in turn, rather than on possible associations of sounds. Implementations of this knowing may therefore raise problems, since acoustical patterns of dvnamical evolution are not well known. The paper addresses the particular case of the []-[lj] and [n]-[nj] acoustical differences. The data show that the differences to be found are mainly related to reorganisations of the time function.