  Since the seminal work by H.L.F. Helmholtz in 1863, to understand the basic
principles of hearing has been a great, but still unresolved, challenge for
physicists. Some time ago, it has been pointed out (Egu\'{\i}luz et al., Phys.
Rev. Lett. 84, 5232, 2000) that the generic mathematical properties of
nonlinear oscillators undergoing a Hopf bifurcation account for the salient
characteristics of hearing. Recently, M.O. Magnasco proposed a model of the
cochlea (Phys. Rev. Lett. 90, 058101, 2003), which employs Hopf-type
instabilities for cochlear amplification. While this model reproduces the
input-output behaviour of the cochlea to some extent, the generated model
responses deviate significantly from physiological measurements. The reason for
the discrepancies between model and experiment are due to the critical choice
of the Hopf control parameter close to the bifurcation point ($\mu = 0$). The
question whether the bifurcation parameter has to be chosen critically or
subcritically ($\mu < 0$), is central, and has become the subject of a
scientific debate.In this contribution, we argue that, for sustained input
signals, the control parameter will assume a subcritical value. This leads to
model results that are in close agreement with reported experimental data.
