Spectral and spatial parameter resolution requirements for parametric, filter-bank-based HRTF processing

D.J. Breebaart, F. Nather, A.G. Kohlrausch

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Abstract

The audibility of HRTF information reduction was investigated using a parametric analysis and synthesis approach. Nonindividualized HRTFs were characterized by magnitude and interaural phase properties computed for warped critical bands. The minimum number of parameters was established as a function of the HRTF set under test, the sound-source position, whether overlapping or nonoverlapping parameter bands were used, and whether spectral characteristics were derived from the HRTF magnitude or power spectrum domain. A three-interval, forced-choice procedure was employed to determine the required spectral resolution of the parameters and the minimum requirements for interaural phase reconstruc tion. The results indicated that, for pink-noise stimuli, the estimation of magnitude and interaural phase spectra per critical band is a sufficient prerequisite for transparent HRTF parameterization. Furthermore the low-frequency HRTF phase characteristics can be effi ciently described by a single interaural delay while disregarding the absolute phase response of the individual HRTFs. Also, high-frequency phase characteristics were found to be irrelevant for the HRTFs and the stimuli used for the test. Estimation of parameters in the spectral magnitude domain using overlapping parameter bands resulted in better quality compared to either power-domain parameter estimation or the use of nonoverlapping parameter bands. When HRTFs were reconstructed by interpolation of parameters in the spatial domain, a spatial measurement resolution of about lO~ was shown to be sufficient for high-quality binaural processing. Further reductions in spatial resolution predominantly give rise to monaural cues, which are stronger for interpolation in the vertical direction than in the horizontal direction. The results obtained provide clear design criteria for parametric HRTF processing in filter-bank-based applications such as MPEG Surround.
Original languageEnglish
Pages (from-to)126-140
Number of pages15
JournalJournal of the Audio Engineering Society
Volume58
Issue number3
Publication statusPublished - 2010

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