The shape of the nonlinearity generating the combination tone 2f1-f2

If the level behavior of the cubic difference tone is explained by a static nonlinear characteristic, the correspondence between this characteristic and certain components and quantities of the basilar membrane must be clarified. This is attempted here for a nonlinearity compatible with the idea of an active undamping feedback mechanism saturating at high levels. The relation between asymptotic behavior of the nonlinearity and the measured CDT level dependence is established. Agreement with psychoacoustic data requires a very "softly" compressing characteristic; linear or logarithmic asymptotes are ruled out. The psychoacoustically known level dependence is well reproduced for small primary-frequency differences by cancellation experiments with a digitally simulated basilar-membrane model.