Investigation of ITD Symmetry in Measured HRIRs

Acoustical Science and Technology, 2003

This paper reviews development of spatial auditory display technology based upon 20 years of research evaluating digital filters designed to spatially position auditory images associated with sound sources presented via earphones. The motivation for this review was to attempt to provide clarification regarding some of the issues and assumptions that underlie such research-driven binaural technology development. After a general discussion of research goals and methods, instructive research results are presented to underscore the main points, especially with regard to questions that could serve to stimulate further useful work on directional filter design. These include questions of how best to customize filters for individual users, and, conversely, how to optimize filters for general use. Also considered are the related questions of how best to evaluate the performance of generic Head-Related Transfer Functions (HRTFs), in contrast to those that are measured for the use of a specific individual. At the heart of this review is a focus on the methods that are most appropriate for the evaluation of auditory imagery resulting from synthetic sound spatialization. While a primary goal for binaural synthesis is to spatially position an auditory image, methods typically employed to study the ability of human listeners to spatially localize an actual sound source address only a narrow subset of the issues that are important to the development of adequate spatial auditory display technology.

2019

Previous literature demonstrates two key components required for the accurate reproduction of a 3-dimensional sound field over headphones: head-related transfer functions (HRTFs) and headphone compensation filters (HCFs). This study seeks to supplement an already extensive body of work with a new methodology for the capture and evaluation of individualized binaural room impulse responses (BRIRs) and HCFs. The results of a double-blind listening test corroborate earlier findings regarding the interaction of BRIR and HCF source on binaural audio quality. Finally, the perceptual advantages of a fully individualized binaural rendering procedure are reported.

Research on Biomedical Engineering, 2016

The present work aims to develop statistical models for the psychoacoustic behavior of human beings in lateralization judgments of binaural acoustic stimuli, as a function of Interaural Time Delay (ITD) and Interaural Amplitude Difference (IAD) for several Sensation Levels (SL). Such models intend to contribute to a deep comprehension of the perception or recognition mechanism which permits listeners to decide whether a source of a sound is located on the right or on the left side of their medial plane. Methods: Numerous lateralization judgments are accomplished through a computer controlled experiment setup in order to investigate the transduction mechanism beneath them. The statistical treatment of the psychoacoustic data obtained has been performed by Two and Three Factors-Probit (Probability Unit) Analysis. Results: The Probit Analysis makes it possible to obtain the model coefficients and to fit 'Probit Planes and Surfaces' to the experimental data in order to study and predict the simultaneous effects produced by ITD and IAD in the listeners' psychoacoustic perceptions at several Sensation Levels (SL). Conclusion: The approach used here is appropriate for the analysis of this kind of binary response and it also offers a simple way to obtain psychophysical responses that can be related to neurophysiological phenomena. It is argued that this fact may lead to another way to access neural information through psychoacoustic experiments, without needing invasive methods.

2010

In the most demanding virtual auditory display applications, in which individualised Head Related Transfer Functions (HRTFs) are used for the presentation of virtual sound sources via headphones, there is controversy regarding how important it may be for individualised Headphone Transfer Function (HpTF) measurements to be used in equalizing the headphone response for each listener. In order to test what impact the use of such individualized HpTF-based correction might have on directional judgments, filtered noise bursts were presented with and without such headphone correction during a test of front/back hemifield discrimination for virtual sound sources positioned on six sagittal planes offset from the median plane by 15 o , 30 o , and 45 o to either side. While perfect discrimination performance was observed given repeated two-interval forced choice discrimination trials in which a pair of short noise bursts were presented using individualised HRTFs, within-trial variation in the spectrum of the source submitted to HRTF-based processing made the task quite difficult, reducing performance to chance levels for 7 of the 17 listeners tested. For the remaining listeners who showed above-chance performance under all conditions tested, performance levels were well below the perfect performance that had been observed when the spectrum of the HRTFprocessed source was held constant. Through inter-stimulus variation in source spectra, which functioned to remove the so-called "known-source-spectrum ceiling effect" associated with simple laboratory tests of virtual auditory display technology, it was possible to show that front/back discrimination performance was clearly affected when sources were processed using headphone correction filters that were based upon a each individual's measured HpTF.

Revista Brasileira de Engenharia Biomédica, 2013

The aim of this work is to present a physical implementation of a noninvasive methodology to analyze the directional sensitivity of human auditory system. A computer controlled experiment setup has been designed and developed to study the behavior of human subjects under the presentation of interaural time delays and interaural amplitude differences for several sensation levels. Methods: The proposed methodology comprises: the application of trains of low-pass fi ltered narrow pulses as acoustic binaural stimuli; the automatic, simultaneous and random variation of interaural time delays and interaural amplitude differences; the absence of human interference along the experimental sessions, except for the decision of the listener under test; the minimization of adaptation effects. Results: Numerous lateralization judgments have been accomplished in order to investigate the transduction mechanism which allows deciding which side of subjects medial plane the source of binaural acoustic stimuli is located in. The behavior of decision time with the order of judgment, the sensation levels and the interaural differences in time and amplitudes has been analyzed. Conclusion: The noninvasive, reliable and automatic approach here presented allows obtaining psychophysical responses associated to the neuro-physiological phenomena underneath lateralization capability.

2012

In this work the importance of individualization in binaural technique is investigated. The results extend the present knowledge on the efficient measurement of individual head-related transfer functions (HRTFs) and highlight the importance of individual equalization filters in binaural reproduction, using both loudspeakers and headphones. Moreover, an integrated framework for the calculation of such equalization filters is presented. An innovative measurement setup was developed to allow the fast acquisition of individual HRTFs. The hardware was designed to be compatible with the range extrapolation technique, which makes the description of the HRTF's distance-dependence possible. Major speedup was obtained by optimizing the multiple exponential sweep method. An individual HRTF dataset with approximately 4000 directions can be measured in less than 6 minutes with this new setup. Crosstalk cancellation (CTC) filters are required when playing back binaural signals via loudspeakers. To allow listeners to freely move their heads, switching between multiple loudspeakers is required and the CTC filters must be constantly updated according to the tracked head position. Filter calculations are carried out in frequency-domain for speed reasons. To impose causality constraints to the regularized frequency-domain calculations, a CTC filter calculation framework was proposed, which incorporates a new approach for the multi-channel minimum-phase regularization. This framework also addresses the switching between active loudspeakers through the use of a weighted filter calculation. A sound localization test showed that individualized CTC systems provided performance similar to that from binaural listening while nonindividualized CTC systems provided significantly lower localization performance. To deliver an authentic auditory impression without additional spectral coloration, binaural reproduction via headphones must be adequately equalized. Such equalization filters are obtained by inverting the headphone transfer function, which varies among listeners and individual fitting. To cope with these variations, a robust individual headphone equalization method was proposed. Perceptual tests showed that, in all but one of the tested situations, no audible differences between the original sound source and its binaural auditory display could be perceived. List of References Acknowledgments Curriculum Vitae List of Figures XV 6.10 Histogram showing the distribution of errors in the 3-AFC discrimination task over different target directions for noise as stimulus condition. The error rate was normalized by the frequency each stimulus was presented at each condition.

Ear and hearing, 2015

In bilateral cochlear implant users, electrodes mapped to the same frequency range in each ear may stimulate different places in each cochlea due to an insertion depth difference of electrode arrays. This interaural place of stimulation mismatch can lead to problems with auditory image fusion and sensitivity to binaural cues, which may explain the large localization errors seen in many patients. Previous work has shown that interaural place of stimulation mismatch can lead to off-centered auditory images being perceived even though interaural time and level differences (ITD and ILD, respectively) were zero. Large interaural mismatches reduced the ability to use ITDs for auditory image lateralization. In contrast, lateralization with ILDs was still possible but the mapping of ILDs to spatial locations was distorted. This study extends the previous work by systematically investigating the effect of interaural place of stimulation mismatch on ITD and ILD sensitivity directly and examin...

The Journal of the Acoustical Society of America, 2010

Listeners discriminated changes in either interaural time differences ͑ITDs͒ or interaural level differences ͑ILDs͒ in one noise band ͑the target͒ in the presence or absence of an uninformative spectrally-remote second noise band ͑the interferer͒. The noise bands had center frequencies of 500 and 4000 Hz and bandwidths of 50 and 400 Hz, respectively. When one band was a target, the other served as an interferer. The interferer was presented either diotically or dichotically with ITDs or ILDs that varied randomly across intervals. "Interference" was defined as occurring if the target thresholds were elevated in the presence of an interferer. For ITD discrimination, interference was greater for the 4000-Hz target than for the 500-Hz target, but for ILD discrimination, interference for the 500-Hz target was greater than or equal to that obtained for the 4000-Hz target. Larger interference effects were obtained when the interferer ITD or ILD was randomly varied, revealing that interference can be large not only for high-frequency targets but also for low-frequency targets with high-frequency interferers. The data are consistent with a model in which listeners combine lateral position across frequency with interaural information weighted according to the accuracy with which positions are encoded in each frequency region.

Journal of the Acoustical Society of America, 1978

A madel for the subjective lateral position of 500-Hz tones is presented and compared with experimental lateralization data. Previous papers in this series have explicitly described the auditory-nerve response to these stimuli and proposed a binaural displayer that interaurally compares the auditory-nerve firing times. The outputs of the displayer are postulated to represent the only information about detailed firing times that is available to the brain. In the present paper, lateral-position predictions are obtained by a central nonoptimal weighting of these outputs that depends on the interaural intensity differcnc½ of the tone. These predictions describe the results of !ateralization-matching experiments more accurately and over a wider range of stimulus conditions than previous theories, except for those results which suggest that lowfrequency binaural tones can generate multiple perceptual images. The predictions of our model are also consistent with the results of centering and laterality-eomparison experiments. It is argued that the data discussed in this paper are generally incompatible with theories that propose a peripheral interaction of interaural timing and intensity information such as the latency hypothesis.

2015

In the absence of a well suited measure for quantifying binaural data variations, this study presents the use of a global perceptual distance metric which can describe both HRTF as well as listener similarities. The metric is derived based on subjective evaluations of binaural renderings of a sound moving along predefined trajectories in the horizontal and median planes. Its characteristics and advantages in describing data distributions based on perceptually relevant attributes are discussed. In addition, the use of 24 HRTFs from two different databases of origin allows for an evaluation of the perceptual impact of some database-dependent characteristics on spatialization. The effectiveness of the experimental design as well as the correlation between the HRTF evaluations of the two plane trajectories are also discussed.