Guidelines for high-fidelity hearing aid design can be deduced from known objective and subjective factors. These factors include head diffraction and external-ear resonance, the bandwidth and peak levels required to reproduce live (e.g., orchestral) performances, the nonlinear distortion characteristics of earphones and ears, the masking effect of background noise levels, and the effect of different types of hearing impairments. A simple set of preliminary guidelines results from the assumption that the hearing aid user has only a mild sensorineural hearing loss cochlear origin. Two laboratory hearing aids have been constructed in accordance with such guidelines; one is a practical Over-the-Ear aid with 8-kHz bandwidth, while the other is an In-the-Ear aid with 16-kHz bandwidth. The objective and subjective evaluation of these aids will be discussed briefly. If time permits, a portion of the prerecorded ABA listening test used to obtain fidelity ratings will be demonstated.