Spikes leaving the cochlear can be modeled using gammatones, small waves with an amplitude raise and a decay. The length of these small waves are tuned by the gammatone order. Longer gammatones correspond to longer, ambient sounds, while smaller gammatones represent crackling or impulsive noise. The gammatones used by real ears are fixed physiologically.
With the cat it was found that the gammatones leaving its cochlear are a compromise right between ambient and crackling optimums. Therefore the auditory world of the cat is most effiently represented by the gammatones.
A violin tone represented with a fitting gammatone:
represented with a gammatone of a frequency too low:
and represented with a gammatone of too slow attack:
Coding music in terms of gammatones shows the amount of spikes needed to represent a sound. Using a xylophone sound it was found that at the beginning about 100 spikes per 10 ms are needed, still further on the sound is very well represented using only about 10 spikes per 10 ms. The gammatones here were chosen such that an optimum representation is reached.
Bader, R.: Efficient coding of a xylophone sound using spikogram non-redundent coding. J. Acoust. Soc. Am.123, 3804, 2008.