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

Authors:
Liebich, S.Jax, P.Vary, P.
Book Title:
ITG-Fachtagung Sprachkommunikation
Publisher:
VDE Verlag GmbH
Date:
Oct. 2016
ISBN:
978-3-80074-275-2
Language:
English

Abstract

The hollow perception of the own voice is still one of the major problems of hearing aids. This effect occurs when the ear canal is completely occluded and is thereby called the occlusion effect (OE). It manifests as an amplification of low frequency components. Due to the fact that mechanical approaches, like venting or deep insertion, carry various downsides, we are investigating the compensation by active noise cancellation (ANC). We are applying principles of control theory to create a fixed, i.e. time-invariant, feedback controller. This controller, corresponding to a digital filter, is designed by the mixed-sensitivity H ∞ controller synthesis. For its operation the secondary path, describing the transmission between the internal loudspeaker and the 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 whole design and the evaluation within simulations include acoustical measurements of the real paths. Three different secondary paths have been considered to evaluate the stability and the performance loss in cases of mismatch. The novelty of this approach is the specific consideration of the OE and the uncertainty of the secondary path within the optimization process.

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