A system for hearing assistance devices to assist hearing aid fitting applied to individual differences in hearing impairment. The system is also usable for assisting fitting and use of hearing assistance devices for listeners of music. The method uses a subjective space approach to reduce the dimensionality of the fitting problem and a non-linear regression technology to interpolate among hearing aid parameter settings. This listener-driven method provides not only a technique for preferred aid fitting, but also information on individual differences and the effects of gain compensation on different musical styles.