The present article is based on the fieldwork performed in Brazil, Argentina, Uruguay and Cuba on the prevalence of African rituals and the construction of a data base of images and sounds of the migrations. Both projects have a multiplicity of points in common. In both situations the cultural marks, wich, sometimes, disappeared in the origin countries, emerge like reference of an imagined community. But this is not the central point of this reflection. We concentrated especially in the process of construction and mediation of the anthropological knowledge in these two situations. We study in these two situations the methodologic and epistemologic principles underlying in this investigation marked by the systematic use of media, that is, of technologies of sound and image and mainly of digital technologies in the anthropological investigation and the mediation of the knowledge.