  The open-source CARFAC (Cascade of Asymmetric Resonators with Fast-Acting
Compression) cochlear model is upgraded to version 2, with improvements to the
Matlab implementation, and with new Python/NumPy and JAX implementations -- but
C++ version changes are still pending. One change addresses the DC (direct
current, or zero frequency) quadratic distortion anomaly previously reported;
another reduces the neural synchrony at high frequencies; the others have
little or no noticeable effect in the default configuration. A new feature
allows modeling a reduction of cochlear amplifier function, as a step toward a
differentiable parameterized model of hearing impairment. In addition, the
integration into the Auditory Model Toolbox (AMT) has been extensively
improved, as the prior integration had bugs that made it unsuitable for
including CARFAC in multi-model comparisons.
