English summary: To what extent have oral musical systems been studied? What are the difficulties and problems typically encountered when musical tradition is discussed at the outset, something that is completely foreign to an analyst? What methodologies are available or imaginable to overcome these obstacles? What are the challenges, limitations, and end results of systematic musical processes? Focusing on the study of Jewish-Ethiopian liturgy, this book attempts to answer these questions through a detailed heuristic description. Rather than a method, it is an account of many years of learning completed in Israel and Ethiopia. Beyond the interest it can generate among specialists who respect an unknown heritage in danger of extinction, it is accessible to any reader interested in learning more about the fascinating aspects of Jewish-Ethiopian ethnomusicology. French text. French description: En quoi consiste l"etude approfondie d"un systeme musical oral? Quelles sont les difficultes et les problematiques generalement rencontrees lorsque la tradition abordee est, au depart, totalement etrangere a l"analyste? Quelles sont les methodologies disponibles ou imaginables pour surmonter ces ecueils? Quels peuvent etre les enjeux, les limites et le bilan d"une systematique musicale? En prenant pour objet d"etude les chants liturgiques juifs ethiopiens, cet ouvrage tente de repondre a ces interrogations par le biais d"une description heuristique detaillee. Plutot qu"une methode, il est le temoin d"un apprentissage accompli pendant de nombreuses annees en Israel et en Ethiopie. Au dela de l"interet qu"il peut susciter aupres des specialistes a l"egard d"un patrimoine meconnu en voie d"extinction, il est accessible a tout lecteur desireux d"en savoir plus sur l"ethnomusicologie comme sur ce judaisme ethiopien si fascinant.