Interaural Cross-correlation Research Articles

Effect of frequency bandwidth on interaural cross-correlation in relation to sound image width of reproduced sounds of a violin

This article discusses the effect of frequency bandwidth on the maximum absolute value of interaural cross-correlation coefficient (IACC) in relation to sound image width (also known as auditory source width, ASW). Subjective experiments concerning sound image width were performed using reproduced sounds of a violin. This article shows that separation into 1/24 and more octave bands and averaging IACC values of these frequency bands leads to a higher correlation to sound image width than IACC in broader frequency bands. Moreover the average of 1/ n octave bands of the temporal deviation of interaural time differences and interaural level differences could be confirmed as measures correlating with sound image width.

Age‐related changes in the binaural temporal window.

Substantial data indicate that monaural temporal processing, sound localization ability, and spatial release from masking decline with advancing age. Physiological and psychophysical evidence indicate that the auditory system is quite sensitive to patterns of interaural cross correlation (IACC) as determined by the combined input from the two ears. Here we test the hypothesis that age‐related changes in temporal processing lead to an elongation of the binaural temporal window as measured with an interaural correlation change interval (ICCI) task. The ICCI threshold was measured as a function of the duration change in interaural correlation. Band pass (400–3200 Hz) noise bursts were separated into three segments. Initial and final segments were interaurally uncorrelated while central segments were interaurally uncorrelated in the standard intervals and interaurally correlated in the signal interval. The duration of the central segment was adaptively varied to determine ICCI threshold. The just noticeable difference in static interaural correlation also was measured. The perception of static and dynamic changes in interaural correlation as well as estimates of the equivalent rectangular duration of the binaural temporal window will be compared across groups of younger and older adult subjects.

Subjective diffuseness of music signals convolved with binaural impulse responses

The spatial impression of sound in a hall can be quantified using sound field factors such as the interaural cross-correlation coefficient (IACC) calculated from binaural impulse response (BIR), henceforth denoted by IACC IR. The subjective diffuseness for the listener is a spatial attribute which depends on factors associated both with the source signal and with the actual sound field, and is quantified using the IACC of the signal received by the listener, henceforth denoted by IACC SR. Therefore, the subjective diffuseness in a given hall may change with the music. The aims of this study are to estimate the IACC SR from the IACC IR and the factors, which is obtained from autocorrelation function (ACF) of music signal, and to evaluate the subjective diffuseness by these factors. First, the relationship between the IACC IR and IACC SR was investigated. Second, subjective diffuseness was measured by a psycho-acoustical experiment. As a result, the IACC SR could be estimated from the IACC IR of the BIR and the effective duration ( τ e ) from the ACF of music signal. It was found that the effects of BIRs on subjective diffuseness could be evaluated by IACC IR for almost all subjects, while the effects of music signals could be evaluated by the τ e and the width of the peak at τ=0 ( W ϕ(0) ) of the ACF.

Head-Movement-Aware Signal Capture for Evaluation of Spatial Acoustics

This research incorporates the nature of head movement made in listening activities, into the development of a quasi-binaural acoustical measurement technique for the evaluation of spatial impression. A listening test was conducted where head movements were tracked whilst the subjects rated the perceived source width, envelopment, source direction and timbre of a number of stimuli. It was found that the extent of head movements was larger when evaluating source width and envelopment than when evaluating source direction and timbre. It was also found that the locus of ear positions corresponding to these head movements formed a bounded sloped path, higher towards the rear and lower towards the front. This led to the concept of a signal capture device comprising a torso-mounted sphere with multiple microphones. A prototype was constructed and used to measure three binaural parameters related to perceived spatial impression-interaural time and level differences (ITD and ILD) and interaural cross-correlation coefficient (IACC). Comparison of the prototype measurements to those made with a rotating Head and Torso Simulator (HATS) showed that the prototype could be perceptually accurate for the prediction of source direction using ITD and ILD, and for the prediction of perceived spatial impression using IACC. Further investigation into parameter derivation and interpolation methods indicated that 21 pairs of discretely spaced microphones were sufficient to measure the three binaural parameters across the sloped range of ear positions identified in the listening test.

Exploratory analysis on the binaural characteristics of the rowing sound

Differences between the signals captured at the entrances to the left and right ears are generally quantified by interaural time differences (ITDs), interaural level differences (ILDs) and interaural crosscorrelation (IC). Here, we attempt to gain knowledge on the changes of these interaural parameters during rowing and to evaluate their potential as source of information to determine rowing expertise exclusively from acoustic signals.

Interaural fluctuations and the detection of interaural incoherence. IV. The effect of compression on stimulus statistics

The purpose of this experiment was to determine whether the normalized interaural cross-correlation (CC) model or a model based on interaural phase and level differences can better describe incoherence detection data. The ability to detect interaural incoherence in three sets of reproducible dichotic noises was tested in six listeners. The first set contained noises with a constrained value of the CC and the CC including signal compression. The second set contained noises with a constrained value of the CC including signal compression. The third set contained noises with constrained values in the fluctuations in the interaural differences. Modeling showed that neither the CC model nor the model using the interaural differences could account for the data in any set. Examination of the statistical properties of the stimuli showed that including compression before the calculation of the interaural CC causes a substantial correlation of this metric to the fluctuations in the interaural phase difference. This finding implies that it may be more difficult to discriminate between the common types of binaural models than previously thought.

Characteristics of train noise in above-ground and underground stations with side and island platforms

Railway stations can be principally classified by their locations, i.e., above-ground or underground stations, and by their platform styles, i.e., side or island platforms. However, the effect of the architectural elements on the train noise in stations is not well understood. The aim of the present study is to determine the different acoustical characteristics of the train noise for each station style. The train noise was evaluated by (1) the A-weighted equivalent continuous sound pressure level ( L Aeq), (2) the amplitude of the maximum peak of the interaural cross-correlation function (IACC), (3) the delay time ( τ 1) and amplitude ( ϕ 1) of the first maximum peak of the autocorrelation function. The IACC, τ 1 and ϕ 1 are related to the subjective diffuseness, pitch and pitch strength, respectively. Regarding the locations, the L Aeq in the underground stations was 6.4 dB higher than that in the above-ground stations, and the pitch in the underground stations was higher and stronger. Regarding the platform styles, the L Aeq on the side platforms was 3.3 dB higher than on the island platforms of the above-ground stations. For the underground stations, the L Aeq on the island platforms was 3.3 dB higher than that on the side platforms when a train entered the station. The IACC on the island platforms of the above-ground stations was higher than that in the other stations.

Binaural speech intelligibility as a function of speaker angle and interaural cross-correlation of disturbing noise and reverberation.

Subjective intelligibility tests were carried out that demonstrate that binaural speech intelligibility under adverse acoustic conditions, such as noise and reverberation, improves when listening at an angle, and also depends on the interaural cross-correlation of the disturbance. Speech material was binaurally recorded in an anechoic chamber using an acoustic manikin, from a loudspeaker at different azimuth angles from −60 deg (left) to +60 deg (right) in 15-deg steps. The binaural speech material was contaminated with interaurally correlated and uncorrelated noise and reverberation, and was presented to listeners through headphones. Results indicate advantages of binaural speech intelligibility under adverse acoustic conditions when listening at an angle, relative to listening at 0 deg. Additionally, speech intelligibility improves when the disturbing reverberation has high interaural cross-correlation; while on the other hand, speech intelligibility improves when the disturbing noise has low interaural cross-correlation.

Auditory and Visual Sensations: Yoichi Ando’s theory of architectural acoustics.

Yoichi Ando is a well‐known architectural acoustician who employed genetic algorithms, acoustics, and psychophysical models of listener percepts and preferences to optimize the design of the Kirishima International Concert Hall in Japan. Ando’s recent book [Auditory and Visual Sensations, guest editor P. Cariani (Springer, New York, 2009)] summarizes decades of psychophysical experiments and neurophysiological observations (ABR, SVR, EEG, MEG). This paper will outline Ando’s psychophysics‐based approach to architectural acoustics and his correlation‐based theory of hearing and vision, along with supporting psychophysical and neurophysiological experimental observations. Ando proposes a temporally coded, correlation‐based model of neuronal signal processing in which features of an internal autocorrelation representation subserve “temporal sensations” (pitch, timbre, loudness, duration), while features of an internal interaural cross correlation representation subserve “spatial sensations” (sound location, size, diffuseness related to envelopment). Together these two representations account for the basic auditory qualities most relevant for listening to music and speech in indoor performance spaces. Remarkably, Ando and colleagues have found many analogs of auditory percepts and preferences in vision. These include perception of the missing fundamental of flickering light as well as preferences for flickering lights, oscillatory movements, and texture regularity. Ando’s theory suggests possible common temporal processing mechanisms for hearing and vision.

Down-mixing of multi-channel audio for sound field reproduction based on spatial covariance

This article describes a method for automatic down-mixing multi-channel audio content on the basis of spatial covariance. Such a down-mixing method should be able to convert the signal of the original multi-channel audio system into that for an alternative system with the lesser number of channels, while maintaining the spatial impression of sound. Moreover, it should take into account the listener’s position and transfer function. Wave surface control and convolving the head related transfer function are techniques used in sound field control or reproduction. We consider that the spatial impressions of a sound field, which we perceive through our ears, are reproduced by preserving the relative relationship between observation points even if the wave surface is not completely controlled. Takahashi et al. proposed a new sound field reproduction method that we named “SOund field Reproduction based on sPAtial Covariance” (SORPAC). SORPAC can control the point-to-point covariance in a sound field. We expect that this sound field reproduction method based on spatial covariance can be applied to down-mixing of multi-channel content because SORPAC does not require the listener’s position or transfer function. This article describes SORPAC and its characteristics. We used SORPAC for down-mixing audio content. We confirmed that SORPAC-based down-mixing could accurately reproduce the interaural cross correlation (IACC) in relation to the listener’s position.

An investigation of floor impact sources and perception models of impact sounds

The present work compared the physical and psychoacoustical characteristics of standard impact sources with those of human impacts, and proposed the perception models of annoyance for impact sounds with respect to temporal and spatial aspects. Impact ball (heavy/soft impact source) was selected as an appropriate standard floor impact source simulating real floor impacts based on the objective evaluation and similarity judgment. Then, measurements using impact ball were conducted in a variety of apartment buildings with different floor structure and coverings. Variations in frequency characteristics were found in the measurement results, thus these were classified into three groups, Groups A-C. Differences between Groups A-C were clarified using sound quality metrics. Finally, perception models of impact ball sounds were developed in relation to temporal aspects and spatial characteristics, respectively. When the spatial characteristics kept constant, perceptions of annoyance for impact ball sounds were affected mainly by the differences in fluctuation strength as well as loudness. Another perception model comprised of IACC (Interaural cross-correlation function) was also proposed through auditory experiments. It was found that IACC had an effect on the perception of impact ball sounds with sound pressure level, and the contribution of IACC on perception of impact ball sounds was around 20%

A binaural localization model that resolves front-back confusions through head movements.

It is well known that head movements are instrumental in resolving front/back confusions in human sound localization. A mechanism for a binaural model is proposed here to extent current cross-correlation models to compensate for head movements. The algorithm tracks sound sources in the head-related coordinate system (HRCS) as well as in the room-related coordinate system (RRCS). It is also aware of the current head position within the room. The sounds are positioned in space using an HRTF catalog at 1 deg azimuthal resolution. The position of the sound source is determined through the inter-aural cross-correlation (IACC) functions across several auditory bands, which are mapped to functions of azimuth and superposed. The maxima of the cross-correlation functions determine the position of the sound source, but unfortunately, usually two peaks occur—one at or near the correct location and the second one at the front/back reversed position. When the model is programed to virtually turn its head, the degree-based cross-correlation functions are shifted with current head angle to match the RRCS. During this procedure, the IACC peak for the correct hemisphere will prevail if integrated over time for the duration of the head movement, whereas the front/back reversed peak will average out.

Interaural cross correlation in a sound field represented by spherical harmonics

Spatial impression is an important acoustic quality of concert halls. An accepted objective measure for spatial impression is the interaural cross-correlation (IACC) coefficient. Recently, spherical microphone arrays have been studied for room acoustics analysis and music recordings. This study presents a theoretical formulation for the computation of IACC using spherical-harmonics representations of the sound field, as measured by spherical microphone arrays, and spherical-harmonics representation of head-related transfer functions (HRTFs), taken from HRTF databases. As spherical microphone arrays typically use a finite number of microphones, they may not be able to capture the complete spatial information in a sound field. Therefore, the effect of limited spherical-harmonics order on the accuracy of IACC approximation using the proposed method is studied using simulated and measured data. The method presented in this paper can be further used to study the effect of limited spatial information on the spatial perception of sound fields.

Deconstructing the interaural cross-correlation function.

Because it is a measure of the similarity of signals in a listener’s left and right ears, the long-term interaural cross-correlation (IACC) function within one-third octave bands provides an estimate of auditory envelopment as well as a guide to the ability to localize a sound. The peak height of the IACC, known as the coherence, is particularly relevant. The IACC can be written mathematically in terms of the amplitudes of spectral components in the left and right ears and in terms of the interaural differences in the component phases. The ensemble-average IACC, as measured with an artificial head in real rooms, can be further analyzed in terms of the amplitudes—their statistical distributions and their interaural correlations—and in terms of the interaural phases—their distributions and correlations with amplitudes. The nature of these statistical relationships depends on the frequency range through the ratio of a characteristic wavelength to the head radius. Analysis of this kind helps solve the long-wavelength problem. In the long-wavelength limit, the IACC must be large, but that does not mean that sound localization is good. [Work supported by the NIDCD Grant DC00181.]

Electrophysiological and psychophysical asymmetries in sensitivity to interaural correlation steps

The binaural auditory system’s sensitivity to changes in the interaural cross correlation (IAC), as an indicator for the perceived spatial diffuseness of a sound, is of major importance for the ability to distinguish concurrent sound sources. In this article, we present electroencephalographical and corresponding psychophysical experiments with stepwise transitions of the IAC in continuously running noise. Both the transient and sustained brain response, display electrophysiological correlates of specific binaural processing in humans. The transient late auditory evoked potentials (LAEP) systematically depend on the size of the IAC transition, the reference correlation preceding the transition, the direction of the transition and on unspecific context information from the stimulus sequence. The psychophysical and electrophysiological data are characterized by two asymmetries. (1) Major asymmetry: for reference correlations of + 1 and - 1 , psychoacoustical thresholds are comparatively lower, and the peak-to-peak-amplitudes of LAEP are larger than for a reference correlation of zero. (2) Minor asymmetry: for IAC transitions in the positive parameter range, perceptual thresholds are slightly better and peak-to-peak amplitudes are larger than in the negative range. In all experimental conditions, LAEP amplitudes are linearly related to the dB scaled power ratio of correlated ( N 0 ) versus anticorrelated ( N π ) signal components. The voltage gain of LAEP per dB( N 0 / N π ) closely corresponds to a constant perceptual distance between two correlations. We therefore suggest that activity in the auditory cortex and perceptual IAC sensitivity are better represented by the dB-scaled N 0 / N π power ratio than by the normalized IAC itself.

Subjective evaluation of heavy-weight floor impact sounds in relation to spatial characteristics

This study investigated the effect of a spatial factor, the magnitude of interaural cross-correlation (IACC) function, on subjective responses to heavy-weight floor impact sounds. Heavy-weight impact sounds were generated by a heavy/soft impact source (impact ball) in real apartments, so that impact sound pressure levels (SPLs) (L(Amax)) and IACC could be analyzed. Just noticeable differences (JNDs) of impact SPL and IACC were investigated through the use of impact ball sounds. JNDs were determined by the criteria of 75% correct answers by participants, and it was found that JNDs of impact SPL and IACC were around 1.5 dB and 0.12-0.13, respectively. In addition, the annoyance caused by an impact ball was evaluated by changes in these two parameters. The results show that annoyance increased with increasing impact SPL and with decreasing IACC; the contributions of the two parameters to the scale value of annoyance were 79.3% and 20.4%, respectively. This indicates that the effects of IACC should be considered for the evaluation of annoyance, and the subjective response to impact ball sounds can be improved by controlling IACC, as well as impact SPL.

Inter-aural cross correlation in a sound field represented by spherical harmonics.

Spaciousness is an important acoustic feature of concert halls. An accepted measure for spaciousness is the inter-aural cross-correlation (IACC), which employs the transfer function from a source in the hall to the two ears of a listener, the latter referred to as head-related transfer functions (HRTF). Recently, spherical microphone arrays have been studied for room acoustics analysis and music recordings. As these arrays typically use a finite number of microphones, they may not be able to capture the spatial information required for complete spatial analysis or for sound reproduction with realistic spaciousness. This study proposes the use of spherical harmonics representations for both the HRTF data and the sound field data, facilitating IACC analysis for sound fields represented by a finite order in the spherical harmonics domain. The effect of limited spherical harmonics order on the spaciousness of various sound fields is finally studied using simulated and measured data.

Sound segregation based on temporal envelope structure and binaural cues

The ability to segregate two spectrally and temporally overlapping signals based on differences in temporal envelope structure and binaural cues was investigated. Signals were a harmonic tone complex (HTC) with 20 Hz fundamental frequency and a bandpass noise (BPN). Both signals had interaural differences of the same absolute value, but with opposite signs to establish lateralization to different sides of the medial plane, such that their combination yielded two different spatial configurations. As an indication for segregation ability, threshold interaural time and level differences were measured for discrimination between these spatial configurations. Discrimination based on interaural level differences was good, although absolute thresholds depended on signal bandwidth and center frequency. Discrimination based on interaural time differences required the signals' temporal envelope structures to be sufficiently different. Long-term interaural cross-correlation patterns or long-term averaged patterns after equalization-cancellation of the combined signals did not provide information for the discrimination. The binaural system must, therefore, have been capable of processing changes in interaural time differences within the period of the harmonic tone complex, suggesting that monaural information from the temporal envelopes influences the use of binaural information in the perceptual organization of signal components.

Computational Auditory Scene Analysis: Principles, Algorithms and Applications

First Page

On the minimum audible difference in direct-to-reverberant energy ratio

The goals of this study were to measure sensitivity to the direct-to-reverberant energy ratio (D/R) across a wide range of D/R values and to gain insight into which cues are used in the discrimination process. The main finding is that changes in D/R are discriminated primarily based on spectral cues. Temporal cues may be used but only when spectral cues are diminished or not available, while sensitivity to interaural cross-correlation is too low to be useful in any of the conditions tested. These findings are based on an acoustic analysis of these variables and the results of two psychophysical experiments. The first experiment employs wideband noise with two values for onset and offset times to determine the D/R just-noticeable difference at -10, 0, 10, and 20 dB D/R. This yielded substantially higher sensitivity to D/R at 0 and 10 dB D/R (2-3 dB) than has been reported previously, while sensitivity is much lower at -10 and 20 dB D/R. The second experiment consists of three parts where specific cues to D/R are reduced or removed, which enabled the specified rank ordering of the cues. The acoustic analysis and psychophysical experiments also provide an explanation for the "auditory horizon effect."