Harmonic analysis of exponential nonlinear devices and validity of THD in judging nonlinearities

Derivations of generalized closed-form harmonic equations for a family of polynomial-approximated and parameterized exponential nonlinear devices (NLDs) are presented. The application of this research is for nonlinear signal processing based psychoacoustic bass enhancement systems. The derived harmonic equations are used to compute THD scores analytically to show that even though the nonlinear curves are different, which may cause different perceptual effects, the THD scores turn out to be exactly the same for all six exponential NLDs. The insights gained from this mathematical analysis indicate that, even without linking to perceptual attributes such as audio quality or nonlinear distortion perception, THD is not a suitable metric to judge or measure the quantitative degrees of nonlinear curves

Objective Perceptual Quality Assessment for Self-Steering Binaural Hearing Aid Microphone Arrays

In this study a self-steering beamformer with binaural output for a head-worn microphone array is investigated in simulated and realworld conditions. The influence of the underlying sound propagation model on the estimation accuracy of the direction of arrival (DOA) estimation algorithm and the overall performance of the combined DOA-beamformer-system is evaluated. For this, technical performance measures as well as objective quality measures based on perceptual models of the auditory system are used. The self-steering beamformer showed better performance than a beamformer with fixed look-direction for SNR values above-2 dB if the propagation model includes at least a coarse head model. Index Terms — Direction of arrival estimation, Array signal processing, Noise Reduction, Hearing aids, Perceptual audio quality estimation 1

Development and Objective Perceptual Quality Assessment of Monaural and Binaural Noise Reduction Schemes for Hearing Aids Von der Fakultät für Mathematik und Naturwissenschaften der Carl-von-Ossietzky-Universität Oldenburg

People with hearing impairment have great difficulties communicating in noisy and reverberant environments. They usually require a higher signal-to-noise ratio (SNR) to achieve the same listening performance as normal hearing people. But even for normal hearing people a noise reduction is desirable in these environments, especially when using modern communication systems such as mobile phones, handsfree devices, or teleconferencing systems. Hence, the development and evaluation of noise reduction algorithms is an active field of research. To achieve the maximum performance and subjective benefit, these algorithms generally need to be evaluated with objective measures that should be based on auditory models in order to predict human perception as closely as possible. The current dissertation contributes to this field by adding yet another dimension to the problem-binaural hearing (i.e., listening with two ears). As a starting point of this thesis, some frequently used objective performance measures and novel objective measures based on recent knowledge of the auditory system are reviewed. Using subjective listening tests on signals processed by monaural noise reductio