Active Cancellation of the Occlusion Effect in Hearing Aids by Time Invariant Robust Feedback

The hollow perception of the own voice is still one of the major problems of hearing aids. This "occlusion effect" (OE) occurs when the ear canal is completely covered and manifests as an amplification of low frequency components. We are investigating the compensation of this effect by active noise cancellation (ANC). A time-invariant feedback controller, corresponding to a digital filter, is designed by the mixed-sensitivity Hoo controller synthesis. The secondary path, describing the transmission between internal loudspeaker and internal microphone, is of great importance. The synthesis requires models of this secondary path, its uncertainty and an objective function for the desired overall system transfer function. The objective function is fitted to the individual OE. The design and the evaluation within simulations include acoustical measurements of the real paths. The novelty is the specific consideration of the OE and the uncertainty of the secondary path within the optimization process.