Comb filters composed in a parallel or a serial way are a popular part of delay-line based artificial reverberators. Because the analysis of a complex comb filter structure can be tedious, there is a need for transforming such a structure into a compact and general representation. For this a transformation into the feedback delay network (FDN) filter structure is proposed as it is a general and well established framework to investigate the acoustic properties of the filter and therefore allows to compare different approaches.