Essential nonlinearities in hearing

Our hearing organ, the cochlea, evidently poises itself at a Hopf bifurcati on to maximize tuning and amplification. We show that in this condition sev eral effects are expected to be generic: compression of the dynamic range, infinitely sharp tuning at zero input, and generation of combination tones. These effects an "essentially" nonlinear in that they become more marked t he smaller the forcing: there is no audible sound soft enough not to evoke them. All the well-documented nonlinear aspects of hearings therefore appea r to be consequences of the same underlying mechanism.