This disclosure relates to measurement of maximum stable gain of a hearing assistance device, including but not limited to hearing aids, as a function of frequency. The III-Nitride device includes a III-Nitride buffer layer situated over a substrate, the III-Nitride buffer layer having a first bandgap. A second flexible substrate extends from, and is continuous with, the second circuit board. Each system is enabled to leverage internal call control advanced features to enhance overall user experience.