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Estimation of the Phase Response of Auditory Filters

Authors Zenke, K.
Year 2014
Thesis Type Master's thesis
Topic Audio Signal Processing
Abstract It has often been assumed that the human auditory system is insensitive to differences in the relative phases of spectral components of a multicomponent sound. Recent studies have proven this wrong. Especially at higher frequencies and for signals with a spectral range covering a single auditory filter, strong phase effects can be observed. The project BiPhase at the Acoustics Research Institute in Vienna involves a series of studies aiming to better understand human phase sensitivity. In particular, different hypotheses about the mechanisms underlying phase effects are studied by testing both normal-hearing and hearing impaired subjects. A new approach for studying phase effects, based on measures of the sensitivity to interaural time differences, is tested in addition to the standard approach based on a masking task. As part of the BiPhase project, this master thesis developed and evaluated a method to measure the cochlear phase response that is applicable in cases of nonuniform phase curvatures of underlying auditory filters, such as occurring in hearing-impaired listeners. The underlying assumption was that stimuli with phase relations causing a more peaky internal temporal representation, after passing the phase response of auditory filtering, cause a stronger ITD cue and are thus more lateralized than flat waveforms. Variation of the phase relations of the stimulus should thus enable to infer the phase response of the auditory filters. The experiment used multicomponent harmonic stimuli with variable phases based on Schroeder phase harmonic complexes. The stimuli were presented with a large envelope ITD. In two consecutive stages the most lateralized stimuli were determined individually for each subject. Four out of eight subjects appeared to show some systematic differences between phase configurations. While the results show a large amount of inter-subject variability, the curvature of the estimated phase response appears to be positive for most subjects, which is consistent with other studies.
Supervisors Höldrich, R., Laback, B.