1. An apparatus for grouping temporal segments of an audio piece, which is structured into main parts repeatedly occurring in the audio piece, into various segment classes, wherein a segment class is associated with a main part, comprising: a provider for providing a similarity representation for the segments, wherein the similarity representation for each segment comprises an associated plurality of similarity values, wherein the similarity values indicate how similar the segment is to every other segment of the audio piece; a calculator for calculating a similarity threshold value for a segment using the plurality of similarity values associated with the segment; and an assigner for assigning a segment to a segment class when the similarity value of the segment meets a predetermined condition with. reference to the similarity threshold value.