Interaural Cross-correlation Research Articles

Trading of intensity and interaural correlation cues in the perception of loudness

When a signal is added to noise in the NoSπ binaural configuration, a reduction in interaural cross‐correlation (IACC) occurs at the signal frequency. Increases in tone intensity produce decreases in IACC. Consistent with this relationship, direct manipulations of IACC can result in the perception of an added signal and progressive reduction in IACC produces progressive increases in the loudness of this signal [Culling et al. 2001 J. Acoust. Soc. Am. 110, 1020‐1029]. In the present study, a narrow sub‐band of noise (460‐540 Hz) embedded within a broadband (0‐3 kHz) diotic noise was manipulated in both intensity and IACC in a 3‐interval, odd‐one‐out task. In the reference intervals, IACC was zero and the spectrum was flat. In the target interval, both the IACC and the intensity of the target band were incremented. These increases have opposing effects on loudness. Correct identification of the target interval followed a U‐shape as a function of the size of intensity increment. The minimum of the function was at chance performance, indicating that the opposing cues were fully traded.

The salience of interaural temporal disparities (ITDs) conveyed by high-frequency signals is determined by the temporal features of their ongoing envelopes

Many studies of binaural hearing reveal that envelopes of complex, high-frequency stimuli convey useful interaural time differences (ITDs). Envelope-based ITDs have, typically, been found to be less "potent" than those conveyed by low-frequency waveforms. When considering such findings, Blauert, in his classic textbook, noted that monaural, peripheral processing would result in 1) low-frequency inputs to the binaural processor that are essentially half-wave rectified versions of the input waveforms and 2) high-frequency inputs that are essentially full-wave rectified versions of only the envelopes of the input waveforms. Taking this into account, Blauert, echoing Colburn and Esquissaud (1976), surmised that low-frequency signals would ultimately convey "more distinct time cues" having greater "transient features" than would high-frequency signals and, therefore, be expected to provide more precise ITD information. By using high-frequency "transposed" stimuli having envelopes constructed to provide "more distinct time cues" we have shown in a variety of experimental contexts that the potency of envelope-based ITDs, can rival that measured with low-frequency stimuli. Our most recent experiments use "raised sine stimuli" in order to vary directly the temporal features of the envelope waveform including its "sharpness," "off-time," and interaural cross-correlation function. The new data will be discussed in terms of Blauert's insight.

Effects of spatial factors of speech, noise, and reverberation sounds on listening difficulty

It is well known that the amount of auditory masking in binaural listening is affected by spatial factors of signal and masking sounds such as the degree of interaural cross-correlation and the arriving direction. The amount of auditory masking for speech signal are usually measured using speech intelligibility tests. However, in the sound fields that appears in everyday life, speech intelligibility are usually close to 100%. Therefore, it was unclear how much the effects of spatial factors on speech communication in everyday life are. Listening tests were performed to clarify the effects of spatial factors on listening difficulty ratings [M. Morimoto et al., J. Acoust. Soc. Am. 116, 1607-1613 (2004)] focussing on the degree of interaural cross-correlations of speech, noise, and reverberation sounds, and on the arriving direction of speech signal. The two spatial factors were controlled by several loudspeakers which are horizontally installed in an anechoic room. The results of listening tests showed that the effects of the two spatial factors on listening difficulty ratings decreased with improving listening conditions, and the effects can be ignored in the sound fields that often appears in everyday life.

Effects of interaural cross-correlation of speech and background noise on listening difficulty

Effects of interaural cross-correlation of speech and background noise on listening difficulty

Acoustical parameters used for the subjective assessment of musical performance spaces

The problem of evaluating the subjective acoustical quality of a performance space through studying the value of measurable acoustical parameters is yet to be fully solved. As a contribution to its solution this paper aims to determine whether any relationships exist between the various acoustic parameters most often considered. The acoustical parameters that are topical for this study are in the number of three. The first of these parameters is the Inter-Aural Cross-Correlation Coefficient (IACC), which is a measure of the diffuseness of the sound field in the room. Then the Early Lateral Energy Fraction (ELEF), or a related measure, the Spaciousness (S), is used for estimating the relative amount of early sound energy reaching the listener from lateral incidence. And lastly the Initial Time Delay Gap (ITDG), which is a temporal factor and an indicator of the rapidity of early echoes for contributing to the early signal build-up at following the direct signal. For the evaluation of these parameters, the impulse response, IR, of the investigated enclosure is necessary. In room acoustical contexts the IR of a room is defined as the response that would be recorded by a microphone in response to a sharp and intense sound signal emitted within the enclosure. For the sake of calculation convenience a medium sized rectangular room is considered in this study and which represents a coarse approximation to a small performance hall. The theoretical model used for evaluating the IR makes a combination of the image sources method for wave reflections at the hard surfaces, and an exact model accounting for the diffraction of waves at the corners of the balconies. Furthermore, and in view of a more realistic determination of, especially the IACC, the phenomenon of sound scattering by the head of the listener is also taken into account. The variation of the value of the acoustic parameters with the position within the room at a constant height position for a presumed listener's ears is then presented in three-dimensional plots. Furthermore, psychoacoustical experiments have shown that the early part of the IR is decisive for the subjective assessment of performance spaces, and further, that the low frequency components of a signal have an important contribution to the feeling of spaciousness. Therefore, a low frequency filtering of the early part of the IR was accomplished for the needs of this study. As a completion to this study, an attempt has also been made toward enhancing the existence of some possible correlation between the various parameters investigated herein. As a result, simple relations may in fact be established between these parameters, and the usefulness of these relationships may find applications in subjective room acoustical assessments for instance for estimating one of these parameters, when inaccessible, from knowing the value of any of the two other ones.

Feature Extraction for the Prediction of Multichannel Spatial Audio Fidelity

This paper seeks to present an algorithm for the prediction of frontal spatial fidelity and surround spatial fidelity of multichannel audio, which are two attributes of the subjective parameter called basic audio quality. A number of features chosen to represent spectral and spatial changes were extracted from a set of recordings and used in a regression model as independent variables for the prediction of spatial fidelities. The calibration of the model was done by ridge regression using a database of scores obtained from a series of formal listening tests. The statistically significant features based on interaural cross correlation and spectral features found from an initial model were employed to build a simplified model and these selected features were validated. The results obtained from the validation experiment were highly correlated with the listening test scores and had a low standard error comparable to that encountered in typical listening tests. The applicability of the developed algorithm is limited to predicting the basic audio quality of low-pass filtered and down-mixed recordings (as obtained in listening tests based on a multistimulus test paradigm with reference and two anchors: a 3.5-kHz low-pass filtered signal and a mono signal)

The impact of variation in low-frequency interaural cross correlation on auditory spatial imagery in stereophonic loudspeaker reproduction

Several attributes of auditory spatial imagery associated with stereophonic sound reproduction are strongly modulated by variation in interaural cross correlation (IACC) within low frequency bands. Nonetheless, a standard practice in bass management for two-channel and multichannel loudspeaker reproduction is to mix low-frequency musical content to a single channel for reproduction via a single driver (e.g., a subwoofer). This paper reviews the results of psychoacoustic studies which support the conclusion that reproduction via multiple drivers of decorrelated low-frequency signals significantly affects such important spatial attributes as auditory source width (ASW), auditory source distance (ASD), and listener envelopment (LEV). A variety of methods have been employed in these tests, including forced choice discrimination and identification, and direct ratings of both global dissimilarity and distinct attributes. Contrary to assumptions that underlie industrial standards established in 1994 by ITU-R. Recommendation BS.775-1, these findings imply that substantial stereophonic spatial information exists within audio signals at frequencies below the 80 to 120 Hz range of prescribed subwoofer cutoff frequencies, and that loudspeaker reproduction of decorrelated signals at frequencies as low as 50 Hz can have an impact upon auditory spatial imagery. [Work supported by VRQ.]

Low-frequency interaural cross correlation discrimination in stereophonic reproduction of musical tones

By industry standard (ITU-R. Recommendation BS.775-1), multichannel stereophonic signals within the frequency range of up to 80 or 120 Hz may be mixed and delivered via a single driver (e.g., a subwoofer) without significant impairment of stereophonic sound quality. The assumption that stereophonic information within such low-frequency content is not significant was tested by measuring discrimination thresholds for changes in interaural cross-correlation (IACC) within spectral bands containing the lowest frequency components of low-pitch musical tones. Performances were recorded for three different musical instruments playing single notes ranging in fundamental frequency from 41 Hz to 110 Hz. The recordings, made using a multichannel microphone array composed of five DPA 4006 pressure microphones, were processed to produce a set of stimuli that varied in interaural cross-correlation (IACC) within a low-frequency band, but were otherwise identical in a higher-frequency band. This correlation processing was designed to have minimal effect upon other psychoacoustic variables such as loudness and timbre. The results show that changes in interaural cross correlation (IACC) within low-frequency bands of low-pitch musical tones are most easily discriminated when decorrelated signals are presented via subwoofers positioned at extreme lateral angles (far from the median plane). [Work supported by VRQ.]

Aurally-adequate time-frequency analysis for scattered sound in auditoria

The goal of this work was to apply an aurally-adequate time-frequency analysis technique to the analysis of sound scattering effects in auditoria. Time-frequency representations were developed as a motivated effort that takes into account binaural hearing, with a specific implementation of interaural cross-correlation process. A model of the human auditory system was implemented in the MATLAB platform based on two previous models [A. Härmä and K. Palomäki, HUTear, Espoo, Finland; and M. A. Akeroyd, A. Binaural Cross-correlogram Toolbox for MATLAB (2001), University of Sussex, Brighton]. These stages include proper frequency selectivity, the conversion of the mechanical motion of the basilar membrane to neural impulses, and binaural hearing effects. The model was then used in the analysis of room impulse responses with varying scattering characteristics. This paper discusses the analysis results using simulated and measured room impulse responses. [Work supported by the Frank H. and Eva B. Buck Foundation.]

Frequency dependency of the relationship between perceived auditory source width and the interaural cross-correlation coefficient for time-invariant stimuli

Previous research has indicated that the relationship between the interaural cross-correlation coefficient (IACC) of a narrow-band sound and its perceived auditory source width is dependent on its frequency. However, this dependency has not been investigated in sufficient detail for researchers to be able to properly model it in order to produce a perceptually relevant IACC-based model of auditory source width. A series of experiments has therefore been conducted to investigate this frequency dependency in a controlled manner, and to derive an appropriate model. Three main factors were discovered in the course of these experiments. First, the nature of the frequency dependency of the perceived auditory source width of stimuli with an IACC of 1 was determined, and an appropriate mathematical model was derived. Second, the loss of perceived temporal detail at high frequencies, caused by the breakdown of phase locking in the ear, was found to be relevant, and the model was modified accordingly using rectification and a low-pass filter. Finally, it was found that there was a further frequency dependency at low frequencies, and a method for modeling this was derived. The final model was shown to predict the experimental data well.

Appropriate frequency bandwidth in measuring interaural cross-correlation as a physical measure of auditory source width

There has been a demand for measuring the degree of interaural cross-correlation (ICC) as a physical measure for auditory (apparent) source width (ASW). Standardization of the measurement has been also discussed by ISO. One of the important problems in measurements of ICC is the selection of frequency bandwidth. Following ISO, ICC is defined with a wide frequency band and generally measured in 1/1 octave bands. This paper reports two experiments that compare ASW with ICC measured by different methods, so as to determine the best physical measure in terms of correlation with the subjective effect. The experimental results show that the use of 1/3 octave bandwidth is preferred to the use of a wide bandwidth and 1/1 octave bandwidth for measuring ICC as a physical measure of ASW.

The effect of various source signal properties on measurements of the interaural crosscorrelation coefficient

Measurements that attempt to predict the perceived spatial impression of musical signals in concert halls typically are conducted by calculating the interaural cross-correlation coefficient (IACC) of an impulse response. The causes of interaural decorrelation are investigated and it is found that this is affected by frequency dependent interaural time and level differences and variations in these over time. It is found that the IACC of impulsive and of narrowband tonal signals can be very different from each other in a wide range of acoustical environments, due to the differences in the spectral content and the duration of the signals. From this, it is concluded that measurements made of impulsive signals are unsuitable for attempting to predict the perceived spatial impression of musical signals. It is suggested that further work is required to develop a set of test signals that is representative of a wide range of musical stimuli.

Discrimination of temporal change in transient interaural cross-correlation coefficient using band-pass-filtered noise burst convolved with simulated impulse responses

Discrimination of temporal change in transient interaural cross-correlation coefficient using band-pass-filtered noise burst convolved with simulated impulse responses

Auditory evoked potentials to changes in interaural cross correlation

The objective of this study is to analyze the representation of specific binaural stimulus features in the human brain and to compare the results to psychoacoustic data. Late auditory evoked potentials to changes in the interaural cross correlation (IACC) of continuous bandpass noise (100–2000 Hz) were recorded, 1000 sweeps per stimulus condition were averaged. In experiment 1 a brief ‘‘binaural gap’’ with a gap IACC was interposed in the noise with a reference IACC. N1 and P2 amplitudes increased with increasing gap duration. For uncorrelated reference IACC (0/1/0 and 0/−1/0 conditions) objective thresholds were comparable to psychoacoustic data. For uncorrelated gap IACC (1/0/1 and −1/0/−1 conditions) objective thresholds were about four times larger than in psychoacoustic measurements. In experiment 2 reference and test interval had the same length of 800 ms and the magnitude of change in IACC was varied. Objective IACC-JNDs are larger for an uncorrelated reference than for IACCs of ±1. For the uncorrelated reference, test IACCs towards +1 elicited larger AEP components than test IACCs towards −1. In contrast to binaural difference potentials used at the brain stem level, employing changes in IACC constitutes a more direct approach to objectively investigate the binaural system in humans.

Interaural cross-correlation coefficient, apparent source width, and time/frequency characteristics of binaural running cross-correlation

The interaural cross-correlation coefficient (IACC) descriptors attempt to characterize in a single number the binaural cross-correlation function at the expense of losing much detail in a manner similar to, but more problematic than, such descriptors as NC, STC, and NRC because much frequency- and rich time-domain information is lost. Recent computer simulations by Mason illuminated these problems and further stimulated the present study. Old binaural impulse recordings run through an analog computer algorithm (drawn from physiological modeling) were re-examined in an attempt to reveal trends and relationships that the current descriptors cannot. Issues of the time and frequency variance of the measured running coefficient are discussed in terms of apparent source width (ASW) for music in Troy Music Hall and simpler spaces.

Evaluation of a model of auditory source width based on the interaural cross-correlation coefficient

A model of human perception of auditory source width has been developed, based on the interaural cross-correlation coefficient (IACC). The following factors differentiate it from more commonly used IACC-based models: the use of a running analysis to quantify variations in width over time; half-wave rectification and low pass filtering of the input signal to mimic the breakdown of phase locking in the ear; compensation for the frequency and loudness dependency of perceived width; combination of a model of perceived location with a model of perceived width; and conversion of the results to an intuitive scale. Objective and subjective methods have been used to evaluate the accuracy and limitations of the resulting model.

Auditory evoked magnetic fields in relation to interaural cross-correlation of band-pass noise

Auditory evoked magnetic fields of the human brain were analyzed in relation to the magnitude of the inter-aural cross-correlation (IACC). IACC of the stimuli was controlled by mixing diotic bandpass and dichotic independent bandpass noise in appropriate ratios. The auditory stimuli were binaurally delivered through plastic tubes and earpieces inserted into ear canals of the nine volunteers with normal hearing who took part in this study. All source signals had the same sound pressure level. Auditory evoked fields (AEFs) were recorded using a neuromagnetometer in a magnetically shielded room. Combinations of a reference stimulus (IACC = 1.0) and test stimuli (IACC = 0.2, 0.6, 0.85) were presented alternately at a constant interstimulus interval of 0.5 s and MEGs recorded. The results showed that the N1m latencies were not affected by IACC; however, the peak amplitude of N1m significantly decreased with increasing IACC.

Annoyance of noise stimuli in relation to the spatial factors extracted from the interaural cross-correlation function

While considering auditory–brain model for subjective responses, effects of spatial factors extracted from the interaural cross-correlation function (IACF) on annoyance of noise stimuli are examined. The previously developed indices to measure sound pressure levels (SPL) and frequency characteristics cannot fully explain the psychological effects of noise. In the first experiment, subjects judged their annoyance by changing fluctuations in the magnitude of interaural cross-correlation function (IACC) and the SPL. In the second, they judged their annoyance by changing fluctuations in the interaural time delay ( τ IACC ) and the SPL. Results show that: (1) annoyance increased by increasing the fluctuations of IACC as well as the SPL, (2) annoyance increased by increasing the fluctuations of τ IACC as well as the SPL.

Computer software for identification of noise source and automatic noise measurement

A new computational system for the environmental noise measurement and analysis has been developed. The system consists of binaural microphones, a laptop PC, and analysing software. A target noise is recorded automatically depending on the specified background noise level, and the acoustical parameters are calculated simultaneously. These functions allow for precise field measurements. The system is equipped with a template-matching algorithm for the identification of noise source. This function was implemented to avoid the effect of an interrupting sound such as voice and wind blowing during a measurement. Noise analyses in this system are based on the model of human auditory system. In addition to the time-series data of sound level, the important acoustical parameters of noise source are extracted from the running autocorrelation function (ACF) and the inter-aural cross-correlation function (IACF). It has been found that those parameters are strongly related to the auditory primary sensations and spatial sensations. Evaluation of the environmental noise based on these functions is another feature of this system. This paper describes the effectiveness of the ACF and the IACF analysis for analysing acoustical properties of noise and for evaluating the subjective response to noise.

크로스토크 제거를 위한 바크스케일 등가 보상 필터를 이용한 음질 향상에 관한 연구

This paper deals a method to deliver more realistic sound by cancelling the cross-talk which is inherent to the 5.1 channel speaker system. The acoustical model for cross-talk cancellation is the free field model. This model minimizes distortion of sound. 1 used the bark scale sound quality compensation which based on psycho-acoustic. For the surround channels, band-limited sound quality compensation is performed in the frequency domain. I also performed the sound qualify assessment test on the traditional 2 channel stereo and 5.1 channel system. This test is performed in the tort chamber which satisfies the ITU-R specifications. 1 uses the IACC(Inter-Aural Cross-Correlation) to determine the preferences of the amateur and the golden ear experts to asses the trans-aural filter. According to the result from the proposed method, I got more the 38dB separation rates with the Dolby standard speaker array. The results on the diffusion by the subjective test with the experts shows 0.4∼0.5 point Increased then before.