Visualization and analysis of multi-channel dynamic range compression in hearing aids

One main functionality of hearing aids is restoring audibility. This means that low sound pressure levels are amplified above the elevated hearing threshold, and higher sound pressure levels do not exceed the individual uncomfortable loudness level (UCL). To this end, hearing aids provide frequency-dependent dynamic range compression which is denoted as hearing aid channels (HACs) in the recently published standard IEC 60118-16. As an increasing number of HACs, among other features, is one main feature to differentiate between price or technology levels, IEC 60118-16 includes a measurement procedure to verify the number of HACs. In this work, we verify this test procedure with a research hearing aid (RHA), and evaluate six commercial hearing aids of three different manufacturers and two technology levels. These results demonstrate the possibilities and limitations of the new test procedure. Furthermore, we introduced an extension of this test procedure with a channel-specific compression setting to overcome limitations and to get a deeper insight into the functionality of HACs in hearing aids. These results show that many HACs of commercial devices are coupled to neighboring frequencies, and that different strategies are used across manufacturers to adapt the number of HACs for different technology levels.