Interaural Cross-correlation Research Articles

The effect of spatial energy spread on sound image size and speech intelligibility.

This study explored the relationship between perceived sound image size and speech intelligibility for sound sources reproduced over loudspeakers. Sources with varying degrees of spatial energy spread were generated using ambisonics processing. Young normal-hearing listeners estimated sound image size as well as performed two spatial release from masking (SRM) tasks with two symmetrically arranged interfering talkers. Either the target-to-masker ratio or the separation angle was varied adaptively. Results showed that the sound image size did not change systematically with the energy spread. However, a larger energy spread did result in a decreased SRM. Furthermore, the listeners needed a greater angular separation angle between the target and the interfering sources for sources with a larger energy spread. Further analysis revealed that the method employed to vary the energy spread did not lead to systematic changes in the interaural cross correlations. Future experiments with competing talkers using ambisonics or similar methods may consider the resulting energy spread in relation to the minimum separation angle between sound sources in order to avoid degradations in speech intelligibility.

Influence of interaural cross-correlation coefficient and loudness level on auditory source width at different frequency

Auditory source width (ASW) is the perceived width of an auditory event of a stimulus, which has complicated relationships with the interaural cross-correlation coefficient, loudness level and frequency. In this paper, the virtual acoustics pointer method is used as the reference signals to investigate the relationship for headphone users. It is found that increasing the loudness level increases the ASW, but with different degrees at different frequencies. The minimum ASW increment appears around 1600 Hz and the maximum occurs around 200 Hz. The average of the ASW increment is approximately 5.4 for 10 phons loudness increment. Decreasing IACC can broaden the ASW, the maximum of the increment of ASW occurs around 400–800 Hz and the average increment is approximately 4.8 for the decrement in IACC of 0.2. A formula is developed by curve fitting to describe the relationship among the three factors and the ASW, which can be used to predict the auditory source width for stereo sound reproduction using headphones and help hearing impaired people perceive more accurate ASW of sound.

Integrating a remote microphone with hearing-aid processing

A remote microphone (RM) links a talker's microphone to a listener's hearing aids (HAs). The RM improves intelligibility in noise and reverberation, but the binaural cues necessary for externalization are lost. Augmenting the RM signal with synthesized binaural cues and early reflections enhances externalization, but interactions of the RM signal with the HA processing could reduce its effectiveness. These potential interactions were evaluated using RM plus HA processing in a realistic listening simulation. The HA input was the RM alone, the augmented RM signal, the acoustic inputs at the HA microphones, including reverberation measured using a dummy head, or a mixture of the augmented RM and acoustic input signals. The HA simulation implemented linear amplification or independent dynamic-range compression at the two ears and incorporated the acoustic effects of vented earmolds. Hearing-impaired listeners scored sentence stimuli for intelligibility and rated clarity, overall quality, externalization, and apparent source width. Using the RM improved intelligibility but reduced the spatial impression. Increasing the vent diameter reduced clarity and increased the spatial impression. Listener ratings reflect a trade-off between the attributes of clarity and overall quality and the attributes of externalization and source width that can be explained using the interaural cross correlation.

No more than “slight” hearing loss and degradations in binaural processing

Listeners having, at most, "slight" hearing loss may exhibit substantial deficits in binaural detection [Bernstein and Trahiotis. (2016). J. Acoust. Soc. Am. 140, 3540-3548; (2018). J. Acoust. Soc. Am. 144, 292-307]. This study assessed whether such listeners also exhibit deficits discriminating interaural temporal disparities (ITDs) or interaural intensitive disparities (IIDs) and whether any deficits observed in those discrimination tasks would be accounted for by the interaural cross-correlation based model that successfully accounts for binaural detection. Thresholds were measured for detection of tones masked by noise in the NoSπ configuration and discrimination of ITD or IID. Gaussian noises (100 Hz-wide), served as maskers in the detection task and as reference and target stimuli in the discrimination tasks. Stimuli were centered at 500 Hz or 4 kHz. The latter were transpositions of stimuli centered at 125 Hz. Results demonstrate that listeners having, at most, slight hearing loss and who exhibit deficits in binaural detection, also exhibit deficits in ITD- and IID-discrimination. Coupled with appropriate decision variables, the cross-correlation-based model that accounts for elevated binaural detection thresholds among such listeners also accounted for their elevated ITD- and IID-thresholds. The deficits in all three tasks appear to stem from increased levels of stimulus-dependent, additive internal noise.

Revisiting perceived intracranial lateralization for stimuli with interaural time differences that are larger than the head

The interaural time difference (ITD) is the primary sound-localization cue for humans. While realistic sound sources have energy across a wide frequency range, the ear performs a narrowband frequency decomposition, and within each band are ambiguities in the interaural cross-correlation (an index of the signal ITD). These ambiguities are thought to be resolved by the approximate consistency of ITDs across frequency, or “straightness.” However, straightness has not been evaluated over a wide range of stimuli. Therefore, normal-hearing listeners reported the intracranial lateralization of narrowband noises and tone complexes to better evaluate across-frequency ITD processing. In a new modification of the typical paradigm, listeners were encouraged to give multiple responses if split images were perceived. ITDs larger than those naturally produced by the head (~750 ms) best demonstrate straightness because across-frequency comparison is necessary to resolve the interaural phase ambiguities, which is why ITDs as large as 1500 ms were applied. Straightness effects reported previously for narrowband noises were replicated, and were broadly similar for complex tones. The extent of lateralization of 1500-ms ITDs and the occurrence of split images were difficult to account for using simple lateralization-based models for smaller ITDs.

Binaural Capability of Locating Sound Sources of Information Signals

The purpose of the work done was to estimate the human binaural capability of locating stereo sound sources of information signals, especially speech, choir singing, and symphonic music as compared to pulse signals. The measurements were conducted in an average-sized hall where sound was emitted by a stereo system consisting of two loudspeakers with the base width of 4.5 m.Based on the results of analysis of existing methods of binaural sound perception modelling, the estimation was performed based on correlational processing of signals recorded using a head dummy placed in various points of the room.For the recording points selected, the maximum time delays between signals arriving at a listener’s left and right ears were calculated, and the interaural cross-correlation functions were obtained. The general functions, especially the peak shift, correlation interval, and peak sharpness (including the conditions when it splits into two individual ones), were analysed. The correlation factor values and levels were calculated. As a result, the conclusions regarding the capability of locating an imaginary sound source were made based on the cross-correlation function factors values, which simplified the application of this method in practice.Based on the results of experiments conducted and on the subjective sensations of perception, the authors have come to the conclusion that a stereophony area has sizes much wider than those assumed earlier from the signal time delay of 1 ms at a receiving stereo pair (representing a shift of an imaginary source towards the ear perceiving the signal earlier).At the same time, it was found that signals with a speech component are much harder to locate than pulse signals. While music signals, especially symphonic music, are close to pulse signals in terms of human locating capabilities.The found patterns have allowed us to introduce adjustments to the stereophony area calculations. Based on the research results, we suggest defining the stereophony zone border by the correlation factor value of 0.5. Given that, the interaural cross-correlation function properties and subjective perception provide for acceptable speech legibility and music transparency. The key conclusion is that this area is quite narrow for speech signals and is actually limited to the time delay of signals arriving at left and right ears – around 1 ms. Music signals have a wider stereophony area defined by the time delay between perception binaural pair components of around 10 ms. Therefore, sizes of a stereophonic sound area ought to be defined with regard to an information signal’s type.Ref. 14, fig. 3, tabl. 3.

Spatial aspects in urban soundscapes: Binaural parameters application in the study of soundscapes from Bogotá-Colombia and Brasília-Brazil

Acoustic environment studies traditionally use monaural energetic parameters as the main acoustic descriptors, which are associated with acoustic comfort and/or noise annoyance. However, under the soundscapes paradigm, it is necessary to explore other acoustic parameters that characterize not only energy levels but also temporal and spatial aspects of the acoustic environments. This paper’s goal is to deepen the study of urban soundscapes, considering the sound sources’ variation in the horizontal plane and determining the relationship of this phenomenon with subjective and descriptive aspects. The objective and subjective aspects of 10 soundscapes in the cities of Brasília (Brazil) and Bogotá (Colombia) were evaluated using fragments of binaural sound recordings. For objective analysis related to spatial behavior of sound sources, Interaural Cross-correlation Functions (IACF) in running and long-term modalities were applied to obtain the Interaural Cross-Correlation (IACC), the Interaural Time Delay (τIACC) and Width of IACC (wIACC). The subjective assessment laboratory tests involved a panel of 25 listeners to evaluate different perceptual attributes and descriptive aspects of the soundscapes. The results indicate that there is a correlation between some binaural parameters derived from the running IACF and different perceptual attributes. Thus, spatial aspects, such as the variation of the sound sources in the horizontal plane, may have implications on perceptual attributes.

Correlation between perception and acoustical parameters in five musical genres

To investigate the influence of sound effects on the perception of musical genres, excerpts from 150 musical pieces of Rock, Jazz, Classical, Ethnographic and Electronic music were compared. In a listening test subjects were asked to judge them in terms of 12 adjectives related to spaciousness, timbre and semantic attributes. Additionally the pieces were analyzed with three methods. To judge the spaciousness the Interaural Cross Correlation (IACC) was calculated. To estimate the audio effect strength an echodensity was defined as the amount of phase fluctuations. To estimate the density of tonal texture a fractal correlation dimension was used. The musical genres clearly sorted along their IACC values with Rock being most ‘mono’ and Classical music most spatial. The echodensity was about the same for all genres except for electronic music where it was considerably larger. The mean fractal correlation dimensions were about four with all genres pointing to a mean textual density for all genres. In terms of perception, the higher echodensity correlated positively with the adjective “artificial” for Electronic music. Additional findings were made.

Identification of perceptually relevant methods of inter-aural time difference estimation.

The inter-aural time difference (ITD) is a fundamental cue for human sound localization. Over the past decades several methods have been proposed for its estimation from measured head-related impulse response (HRIR) data. Nevertheless, inter-method variations in ITD calculation have been found to exceed the known just noticeable differences (JNDs), leading to possible perceptible artifacts in virtual binaural auditory scenes, when personalized HRIRs are being used. In the absence of an objective means for validating ITD estimations, this paper examines which methods lead to the most perceptually relevant results. A subjective lateralization study compared objective ITDs to perceptually evaluated inter-aural pure delay offsets. Results clearly indicate the first-onset threshold detection method, using a low relative threshold of -30 dB, applied on 3 kHz low-pass filtered HRIRs as consistently the most perceptually relevant procedure across various metrics. Several alternative threshold values and methods based on the maximum or centroid of the inter-aural cross correlation of similarly filtered HRIR or HRIR envelopes also provided reasonable results. On the contrary, phase-based methods employing the integrated relative group delay or auditory model were not found to perform as well.

Proportion of effects by head-related transfer function and receiver position variation to interaural cross-correlation values.

Interaural cross-correlation coefficient (IACC) is an objective room-acoustic parameter associated with the spatial impression and subjective quality of the acoustics. This study investigates the proportion of effects on the IACC variance simultaneously by (1) varied head-related transfer function (HRTF) and (2) locally varied receiver positions. The early IACC80 values are estimated from the binaural room simulations in eight room-acoustic conditions varying in room shape, side wall absorption, and receiver distance. Analysis across the combinations of HRTF and receiver positions indicates that below 2 kHz, around two-thirds of total IACC variance is explained by the receiver displacement, and at higher frequencies the HRTF variations dominate the IACC variance.

Effects of two different modeling alternatives of diffusive surfaces on the objective and perceptual evaluation of the simulated sound fields

Different acoustic simulation software have been substantially improved over the last decades accounting for absorptive and diffusive acoustic properties of different surfaces. Whereas the characteristics of the absorptive surfaces have been thoroughly investigated and implemented, the diffusive surface features are still subject to continuous research. So far, the degree of modeling detail of diffusive surfaces, and consequently, the effects that this has on the objective and subjective accuracy of simulations is an open point. In order to give more insight on this aspect, Odeon acoustic simulations have been performed in the model of a variable-acoustic concert hall using a diffusive and a reflective condition of one of the lateral walls. Two different modeling alternatives of the wall diffusive condition have been investigated. Objective acoustic parameters, such as early decay time (EDT), reverberation time (T30), clarity (C80), definition (D50), and interaural cross correlation (IACC), have been compared between the two conditions. Furthermore, a subjective investigation has been performed in order to determine the most accurate modeling alternative of the diffusive surfaces. Although the simulated objective results showed a good match with measured values, the subjective results highlighted significant perceptual differences for different modeling alternatives.

Analysis on decorrelation effect of audio signal in multichannel reproduction

Decorrelation of audio signal is a process that generates two or more incoherent signals from a single input signal, which has many applications in artificial auditory effects, such as broadening the apparent source width (ASW), enhancing the subjective envelopment, producing subjective diffusion in multichannel reproduction, etc. Frequently used decorrelation method is convoluting audio signal with random (or pseudo-random) noise. In this work, we focus on the relationship of reproduction zone of multichannel reproduction with decorrelation degree. Simulation calculation result show that, by changing the decorrelation degree which is measured by the interaural cross-correlation coefficients (IACC) of reproduced signals, the timbre will change when move off the listening center. Listening zone with small timbre deviation (for example, binaural loudness spectra less than 1dB/ERB) relative to center position increase with the value of IACC decrease. But as well known, for good subjective diffusion, the least IACC value does not mean the best effect. There exit a best IACC value range from 0.2~0.4 for different audio signal. Adapting a best IACC value, a reproduction zone across different frequencies can be achieved.

Inter-aural cross-correlation measured during symphony orchestra performance in big concert halls

Spatial impression in concert hall listeners is known to depend on lateral reflections causing differences between the sound at the left ear and the right ear. Such differences can be measured, e.g., by the so-called inter-aural cross-correlation IACC in a binaural signal pair, i.e., a signal pair from microphones placed in the ear canal entrances. IACC data from binaural impulse responses (BRIR) are commonly reported. In contrast, little attention has been paid to running IACC, i.e. IACC(t), during music performance. Therefore, in 2011 this author launched the Binaural Project in 2011 in order to collect binaural signal data from concerts with symphony orchestras. An analysis of IACC(t) from more than 600 minutes of binaural recordings during concerts in many big concert halls is presented. Several famous halls, including Boston Symphony Hall, are included in the data. Among the questions to be answered are Can we observe from the data that concert halls make a difference to IACC(t)? If so—is this variation small or big compared to the variation from one moment to another, bar to bar, movement to movement, from one orchestra to another, and so on? On the other hand, if we cannot observe significant hall-to-hall differences, several new questions would arise, including How can we maintain that listeners are able to perceive hall-to-hall differences in ASW and LEV? And why do not the reported hall-to-hall differences in IACC from impulse responses (ISO-3382) make an observable difference to running IACC(t)?

Identifying a perceptually relevant estimation method of the inter-aural time delay

The Inter-aural Time Difference (ITD) is a fundamental cue for human sound localization. Over the past decades, several methods have been proposed for its estimation from measured Head-Related Impulse Response (HRIR) data. Nevertheless, inter-method variations in ITD calculation have been found to exceed the known Just Noticeable Differences (JNDs), hence leading to possible perceptible artifacts in virtual binaural auditory scenes, even for cases when personalized HRIRs are being used. In the absence of an objective means for validating ITD estimations, this paper evaluates which methods lead to the most perceptually relevant results. A subjective lateralization study compared objective ITDs to perceptually driven inter-aural pure delay offsets. Results clearly indicate the first-onset Threshold detection method, using a low relative threshold of -30 dB, applied on 3 kHz low-pass filtered HRIRs as the most perceptually relevant procedure across various metrics. Alternative threshold values and methods based on the maximum or centroid of the Inter-Aural Cross Correlation of similarly filtered HRIRs or HRIR envelopes also provided reasonable results. On the contrary, phase-based methods employing the Integrated Relative Group Delay were not found to perform as well.

Stimulus coherence influences sound-field localization and fusion/segregation of leading and lagging sounds.

The ability to localize sound sources in reverberant environments is dependent upon first-arriving information, an outcome commonly termed "the precedence effect." For example, in laboratory experiments, the combination of a leading (direct) sound followed by a lagging (reflected) sound is localized in the direction of the leading sound. This study was designed to measure the degree to which stimulus compactness/diffuseness (i.e., coherence as represented by interaural cross correlation) of leading and lagging sounds influences performance. The compactness/diffuseness of leading or lagging sounds was varied by either presenting a sound from a single loudspeaker or by presenting mutually uncorrelated versions of similar sounds from nine adjacent loudspeakers. In separate experiments, the listener's task was to point to the perceived location of leading and lagging 10-ms long low-pass filtered white noises or 2-s long tokens of speech. The leading and lagging stimuli were presented either from speakers located directly in front of the listeners or from speakers located ±45° to the right or left. The results indicate that leading compact (coherent) sounds influence perceived location more so than do leading diffuse (incoherent) sounds. This was true independent of whether the sounds were Gaussian noises or tokens of speech.

Effects of the Distance from a Diffusive Surface on the Objective and Perceptual Evaluation of the Sound Field in a Small Simulated Variable-Acoustics Hall

Simulations of the acoustic effects that diffusive surfaces have on the objective acoustic parameters and on sound perception have not yet been fully understood. To this end, acoustic simulations have been performed in Odeon in the model of a variable-acoustic concert hall. This paper is presented as a follow-up study to a previous paper that dealt with in-field measurements only. As in measurements, a diffusive and a reflective condition of one of the lateral walls have been considered in the room models. Two modeling alternatives of the diffusive condition, that is, (a) a flat surface with high scattering coefficient applied; and (b) a triangular relief modeled including edge diffraction, have been investigated. Objective acoustic parameters, such as early decay time (EDT), reverberation time (T30), clarity (C80), definition (D50), and interaural cross correlation (IACC), have been compared between the two conditions. Moreover, an auditory experiment has been performed to determine the maximum distance from a diffusive surface at which the simulated acoustic scattering effects are still audible. Although the simulated objective results showed a good match with measured values, the subjective results showed that the differences between the diffuse and reflective conditions become significant when model (b) is used.

Objective and perceptual evaluation of distance-dependent scattered sound effects in a small variable-acoustics hall.

Performance spaces are characterized by a complex sound field, due to the presence of absorptive and diffusive surfaces. In situ evaluations of the acoustic effects that these surfaces have on the objective acoustic parameters and on sound perception have not yet been fully understood. To this aim, acoustic measurements have been performed in a variable-acoustic concert hall, the Espace de Projection, at the Institut de Recherche et Coordination Acoustique/Musique. These measurements have allowed the effects of one single wall to be determined. A diffusive and a reflective condition of one of the long lateral walls of the shoebox-like hall have been considered, while the other surfaces have been fixed in absorptive mode. Measurements have been carried out at different distances from the test wall, using an artificial head and an array of omnidirectional microphones. Objective acoustic parameters, such as early decay time, reverberation time (T30), clarity (C80), definition (D50), and interaural cross correlation, have been compared between both conditions. In addition to the objective indexes, a perceptual evaluation has been performed using listening tests that had the purpose of determining the maximum distance from a diffusive surface at which acoustic scattering effects are still audible.

Just noticeable differences of spatial cues in echoic and anechoic acoustical environments.

The perceptual limits for detecting changes in binaural cues also define the boundaries for the perception of differences in spatial impression. This study reports just noticeable differences for interaural time delays (ITDs) and interaural level differences (ILDs) of the early part and for the interaural cross-correlation (IACC) of the early and diffuse part of binaural room impulse responses. The results show that ITDs only allow a high accuracy in localization in anechoic environments, whereas ILDs show a higher robustness against reverberation. Subjects are rather insensitive to changes in IACC, only changes that bring the IACC close to one are detectable.

Evaluating the auralization of a small room in a virtual sound environment using objective room acoustic measures

To study human auditory perception in realistic environments, loudspeaker-based reproduction techniques have recently become state-of-the-art. To evaluate the accuracy of a simulation-based room auralization of a small room, objective measures, such as early-decay-time (EDT), reverberation time, clarity, interaural cross-correlation (IACC), and the speech transmission index were measured in an IEC listening room for 28 source-receiver combinations. The room was then modeled in the room acoustics software ODEON, and the same objective measures were also evaluated for the auralized version of the room. The auralizations were generated using the loudspeaker-based room auralization toolbox (LoRA; Favrot and Buchholz, 2010) and reproduced in a 64-channel loudspeaker array, set up in an anechoic chamber. Differences between the objective measures evaluated in the real and the virtual room were within about twice the just-noticeable differences for most measures, and were comparable to the median results of the study by Favrot and Buchholz, who did not consider the contribution of a real reproduction system. However, the EDT showed considerably higher errors than the other measures, even though medians were similar in the real and auralized room. This suggests that fine details in the early part of the room impulse response may be difficult to reproduce accurately.

Relating interaural difference sensitivities for several parameters measured in normal-hearing and hearing-impaired listeners.

Just-noticeable differences (JNDs) in interaural time delay (ITD), interaural level difference (ILD), and interaural cross-correlation (ICC) were measured with low- and high-frequency noise bands over multiple sessions for 10 normal-hearing (NH) and 11 hearing-impaired (HI) listeners. Individual subject thresholds tended to improve with training then stabilize. Measured JNDs varied over these experienced listeners, for both subject groups and all tasks. Group JNDs were seldom predictable from hearing level. Individual listeners' JNDs were highly correlated across frequency for each task and group, except for ICC in the HI listeners. Further, ITD JNDs almost always significantly correlated with ILD JNDs within a group. Finally, although the ICC JNDs always significantly correlated with the ITD or ILD JNDs for the NH listeners, they often did not for the HI listeners. These findings suggest that little information about binaural sensitivity is added for NH listeners with multiple ITD, ILD, and ICC measures. For HI listeners, however, while ITD and ILD measures are well correlated, information is added with ICC measures. In general, the results suggest that less information is added with JND measures for NH listeners (15 significant correlations) than for HI listeners (six significant correlations).