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Promotionsprüfung von Dr.-Ing. Stefan Liebich

Dr.-Ing. Stefan Liebich berichtete am Vormittag in einem 45-minütigen Vortrag über seine Arbeiten. Am Nachmittag hat er seine mündliche Promotionsprüfung erfolgreich abgeschlossen zum Thema:

"Active Noise and Occlusion Effect Cancellation in Headphones and Hearing Aids"

Abstract: The perception of one's own voice is distorted when telephoning with headsets, or wearing hearing aids. The reason for this is the so-called occlusion effect. The ear canals are completely or partially closed by the headset or hearing aid. The occlusion causes amplification of low frequencies, and attenuation of high frequencies of one's own voice. The unnatural perception of one's own voice and of noise caused by chewing and swallowing are among the most common complaints of users. Furthermore, environmental noise might impair perception. In this thesis, both the unnatural perception of one's own voice and the disturbance by environmental noise are tackled by novel signal processing approaches.

The proposed solution solves the problem of the occlusion effect by actively emitting a compensation signal through the integrated loudspeaker. This novel approach combines methods of active noise cancellation (ANC, Noise Cancelling Headphone) with a personalized design. The binaural headset contains two additional microphones per side, one inner and one outer, to acquire signals for the calculation of the compensation signals.

A combination of feedback and feedforward digital filters allows for either approaching personal silence or a natural perception of one's own voice and the surroundings.

The main contributions are:

  • Novel design concept for ANC / OEC systems which are robust w.r.t. acoustical variations of ear canals and earpiece fittings
  • Novel structure for combined feedback-feedforward filters with adaptive stability control
  • Analysis of variability of acoustic front-end (headset) as well as electronics back-end (digital signal processing incl. AD/DA-conversion) and implications on ANC/OEC performance
  • Real-time implementation, instrumental and auditive evaluations

The achieved ANC performance is comparable to that of a commercial reference system. The OEC performance revealed in both objective measurements and subjective listening tests, significant improvements of the own-voice perception.