The way groups of auditory neurons interact, to code acoustic information is investigated using an information theoretic approach. We develop measures of redundancy among groups of neurons, and apply them to the study of collaborative coding efficiency in two processing stations in the auditory pathway: The inferior colliculus (IC) and the primary auditory cortex (AI). Under two schemes for the coding of t he acoustic content, acoustic segments coding and stimulus identity coding, we show differences both in information content and group redundancies between IC and Al neurons. These results provide for t he first time a direct evidence for redundancy reduction along the ascending auditory pat hway, as has been hypothesized for theoretical considerations [Barlow 1959.2001]. The redundancy effect s under the single-spikes coding scheme are significant only for groups larger than ten cells, and cannot be revealed with the redundancy measures that use only pairs of cells. The results suggest that the auditory system transforms low level representations t hat contain redundancies due t o t he statistical st ructure of natural stimuli, into a representation in which cortical neurons extract rare and independent component of complex acoustic signals, t hat are useful for auditory scene analysis.