Sound quality in hearing devices could be improved by providing acoustic transparency, i.e., electronically creating a listening impression alike to the open ear. This can be achieved by equalizing the hearing device output to conserve the transfer function of the individual open ear as closely as possible. The achievable accuracy is limited by unavailability of individual transfer functions, processing delays, and leakage of external sounds into the ear canal. In the present work, the influence of these limitations on perceived sound quality was assessed. Acoustic scenes as heard through a hearing device were simulated using individually measured transfer functions with an in-ear device and presented through headphones. The sound quality was assessed using a MUSHRA-like framework with normal-hearing subjects and a sound quality model. Equalization to the diffuse-field response of the open ear is shown to be close to optimum in most daily-life situations. Although the benefit of incorporating the individual open-ear response is evident but limited, using knowledge of the individual driver responses and leakage improves the perceived sound quality especially with a vented fit.With appropriate equalization, the influence of the fit and processing delays is of less importance. Sound quality models allow a reasonable prediction of perceived sound quality.
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