The ear is able to detect low-level acoustic signals by a highly specialized system including\na parametric amplifier in the cochlea. This is verified by a numerical mechanical model of the cochlea,\nwhich reduces the three-dimensional (3D) system to a one-dimensional (1D) approach. A formerly\ndeveloped mechanical model permits the consideration of the fluid and the orthotropic basilar\nmembrane in a 1D fluid-structure coupled system. This model shows the characteristic frequency to\nplace transformation of the traveling wave in the cochlea. The additional inclusion of time and space\ndependent stiffness of outer hair cells and the signal level dependent stiffness of the string enables\nparametric amplification of the input signal. Due to the nonlinear outer hair cell stiffness change,\nnonlinear distortions follow as a byproduct of the parametric amplification at low levels constituting\nthe compressive nonlinearity. More distortions are generated by the saturating displacements of the\nstring at high input levels, which can be distinguished from the low-level distortions by the order of\nadditional harmonics. Amplification factors of 15.5 dB and 24.0 dB are calculated, and a change of the\ntraveling-wave mapping is postulated with parametric amplification representing the healthy state\nof the cochlea.
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