The shape of stimulus onset is a distinct feature of many acoustic communication signals. In some grasshopper species the steepness of amplitude rise of the pulses which comprise the song subunits is sexually dimorphic and a major criterion of sex recognition. Here, we describe potential mechanisms by which auditory interneurons could transmit the information on onset steepness from the metathoracic ganglion to the brain of the grasshopper. Since no single interneuron unequivocally encoded onset steepness, it appears that this information has to reside in the relative spike counts or the relative spike timing of a small group of ascending auditory interneurons. The decisive component of this mechanism seems to be the steepness-dependent leading inhibition displayed by two interneurons (AN3, AN4). The inhibition increased with increasing onset steepness, thus delayed the excitatory response, and in one interneuron even strongly reduced the spike count. Other ascending interneurons, whose responses were little affected by onset steepness, could serve as reference neurons (AN6, AN12). Thus, our results suggest that a comparison of both, spike count and first-spike timing within a small set of ascending interneurons could yield the information on signal onset steepness, that is on the sex of the sender.