头相关传输函数幅度谱的听觉空间分辨阈值的分析

提出一种分析头相关传输函数(head-related transfer function,HRTF)幅度谱的听觉空间分辨阈值模型。采用数值计算得到的高空间分辨率HRTF数据,计算了声源空间位置变化引起的HRTF幅度谱的变化,进一步利用Moore响度模型分析双耳响度级差、双耳响度级谱和总响度级等三个听觉感知量的变化。根据现有的3个听觉感知量最小可察觉差异,模型利用双耳响度级差和双耳响度级谱的变化得到的估计结果与心理声学实验一致,因此是一种有效预测听觉空间分辨阈值的方法,可用于为简化虚拟听觉信号处理和数据储存。     

Ambisonics声捡拾与重放音色的双耳听觉模型分析与实验

提出用双耳听觉模型对空间声音色进行分析的普遍方法,并以Ambisonics为例进行了分析。Ambisonics是基于物理声场重构的空间声系统,其最终重构声场误差以及音色改变是由传声器捡拾和重放空间混叠误差共同引起的。采用修正的Moore双耳响度模型计算了Ambisonics重构声场的双耳响度级谱并和目标声场的情况比较,从而定量评价重构声场的音色改变。结果表明,在理想捡拾信号的情况下,无音色改变重放的上限频率和区域大小随Ambisonics的阶数而增加。而对于传声器阵列捡拾的情况,只要阵列的上限频率大于Ambisonics重放的上限频率,在重放的上限频率以下,传声器阵列空间混叠误差对最终重构声场及其感知音色的影响就可以忽略。在此基础上,提出了一种综合考虑捡拾与重放性能的Ambisonics系统优化设计方法。心理声学实验得到了和双耳听觉模型一致的结果,从而也验证了模型分析的有效性。     

Ambisonics声捡拾与重放音色的双耳听觉模型分析与实验

提出用双耳听觉模型对空间声音色进行分析的普遍方法,并以Ambisonics为例进行了分析。Ambisonics是基于物理声场重构的空间声系统,其最终重构声场误差以及音色改变是由传声器捡拾和重放空间混叠误差共同引起的。采用修正的Moore双耳响度模型计算了Ambisonics重构声场的双耳响度级谱并和目标声场的情况比较,从而定量评价重构声场的音色改变。结果表明,在理想捡拾信号的情况下,无音色改变重放的上限频率和区域大小随Ambisonics的阶数而增加。而对于传声器阵列捡拾的情况,只要阵列的上限频率大于Ambisonics重放的上限频率,在重放的上限频率以下,传声器阵列空间混叠误差对最终重构声场及其感知音色的影响就可以忽略。在此基础上,提出了一种综合考虑捡拾与重放性能的Ambisonics系统优化设计方法。心理声学实验得到了和双耳听觉模型一致的结果,从而也验证了模型分析的有效性。      

人工头近场头相关传输函数及其特性

采用球形正十二面体声源及其空间定位系统,测量并建立了KEMAR人工头的近场头相关传输函数(HRTF)数据库。基于数据库分析了近场HRTF在频域和时域随声源距离变化的规律;讨论了用近场HRTF算得的双耳声级差(TLD)和双耳时间差(ITD)所包含的声源距离定位信息。结果表明,测量系统和所得数据具有较好的重复性和准确性,保留了1 kHz以下的低频定位信息。并且,近场HRTF幅度谱和ILD随声源距离的变化明显;用相关法算得2 kHz以下频段的ITD随声源距离略有变化。本文数据库及其分析结果将为声源距离定位的应用提供基础。      

中西方典型乐器音高响度与音色明亮度的研究

为了客观地评价民族乐器与西洋乐器在听觉感知方面的差异,本文利用15种典型的中西方乐器声样本,建立了与音色、响度和音色明亮度有关的15种乐器的感知空间模型,通过这些模型可以预测不同乐器在音高、响度一定时,音色明亮度的感知情况。此外,根据已建立的感知空间模型分别对比弹拨乐器、拉弦乐器和不同类型的吹奏乐器中三种听觉感知属性的变化差异。结果表明,对于中西方典型乐器,音色明亮度随响度的增加而增大,但是响度对音色明亮度的影响程度受到音域和响度范围的影响。民族乐器的音色明亮度随音高的增加而增大,但是西洋乐器的音色明亮度并没有随音高的增加而发生明显的变化。     

个性化头相关传输函数的近似获取——现状和问题

虚拟听觉重放采用头相关传输函数(HRTF)合成双耳声信号,并用耳机重放,以产生所需的空间听觉事件。理想的虚拟听觉重放需要个性化HRTF。个性化HRTF可通过实验测量或数值计算相对地准确获得。然而,测量每个潜在使用者的高空间分辨率HRTF是困难的,而数值计算HRTF的频段往往受限于计算机性能。近年发展了多种HRTF的近似获取方法,并成为热门研究课题,但效果有待验证和提高。本文评述了个性化HRTF近似的研究进展,指出了存在的问题和今后的方向。     

头相关传输函数与虚拟听觉

头相关传输函数(HRTF)是自由场情况下点声源到双耳的声学传输函数,它包含了有关声源的主要空间信息,因而在双耳空间听觉的研究方面有非常重要的意义.作为HRTF的一个重要的应用,虚拟听觉则是近二十年发展起来的新技术,它利用HRTF进行信号处理,模拟出声波从声源到双耳的传输,从而在耳机或扬声器重放中虚拟出相应的空间听觉.虚拟听觉技术在有关听觉的科学实验、通信、多媒体与虚拟现实、家用声重放、室内声学设计等科学研究、工程技术、消费电子领域都有重要的应用价值.近十多年来,国际上有关HRTF和虚拟听觉技术的研究发展很快,已成为声学、信号处理、听觉等研究领域的热门与前沿课题,并已在众多的领域得到应用.     

复杂谐波信号中响度和谱质心的相互影响——响度和谱质心辨别阈的实验研究

根据阈值测量实验和变化一致性测量实验,在单自变量干扰和双自变量干扰两种情况下量化分析响度和谱质心之间的交互关系。研究发现:(1)复杂谐波信号中谱质心对响度的影响强于响度对谱质心的影响;(2)声音的变化方向对被试判断响度和谱质心的阈值存在影响。研究结果进一步呈现了响度和谱质心的定量特征,为听觉属性交互关系的深入研究提供了新的思路。      

重放自由场虚拟源距离信息的动态双耳Ambisonics方法

双耳重放的目标之一是在耳机重放中产生不同方向和距离的虚拟源感知。本文研究了动态双耳Ambisonics重放自由场虚拟源方向和距离信息的简化信号处理方法。该信号处理方法包括两步:第1步是基于目标声场的球谐函数分解,合成采用扬声器的近场Ambisonics重放中逐级重构目标声场的信号;第2步是采用虚拟扬声器重放的方法,用动态头相关函数滤波处理将Ambisonics的扬声器重放信号转换为双耳重放信号并用耳机重放。进一步研究了动态双耳Ambisonics的阶数对定位效果的影响,为简化信号处理提供依据。对重放产生的双耳声压分析表明,5阶动态双耳Ambisonics重放足以提供听觉方向定位和距离感知的重要信息。同时心理声学的实验结果表明,结合声源距离相关的响度因素,5阶动态双耳Ambisonics重放可产生不同方向和1.0 m以下不同近场距离的自由场虚拟源的听觉感知。本文的方法仅需要固定距离的48个均匀空间方向的远场非个性化HRTF处理,实现了信号处理的简化。      

基于个体张量分解与模态的头相关传输函数重构

远场头相关传输函数(HRTF)随声源方向、频率以及个体变化。完整HRTF的数据量很大,且测量或计算每个人的高方向分辨率HRTF是很困难的。本文提出一种从少量方向的测量或计算重构高方向分辨率HRTF的方法。基于HRTF张量分解,远场HRTF可分解为方向模态、频率模态和少量个体模态的张量组合。通过对已有的基线HRTF数据库进行统计分析,可得到与个体无关的方向模态矩阵和频率模态矩阵。而对于任何新的个体,只要少量方向的测量或计算HRTF即可估计出个体模态的变化,并重构出高方向分辨率的HRTF数据。对两个HRTF数据库的计算表明,采用11个个体模态即可表示超过98%的个体相关的HRTF能量变化,并从大约30个方向的测量或计算HRTF重构出高方向分辨率的HRTF幅度。心理声学实验验证了提出的方法。该方法可用于简化个性化HRTF的测量或计算。     

Analysis of the spatial discrimination threshold of head-related transfer function magnitude

A binaural-loudness-model-based method for evaluating the spatial discrimination threshold of magnitudes of head-related transfer function(HRTF) is proposed.As the input of the binaural loudness model,the HRTF magnitude variations caused by spatial position variations were firstly calculated from a high-resolution HRTF dataset.Then,three perceptualrelevant parameters,namely interaural loudness level difference,binaural loudness level spectra,and total binaural loudness level,were derived from the binaural loudness model.Finally,the spatial discrimination thresholds of HRTF magnitude were evaluated according to just-noticedifference of the above-mentioned perceptual-relevant parameters.A series of psychoacoustic experiments was also conducted to obtain the spatial discrimination threshold of HRTF magnitudes.Results indicate that the threshold derived from the proposed binaural-loudness-modelbased method is consistent with that obtained from the traditional psychoacoustic experiment,validating the effectiveness of the proposed method.     

Spatial symmetry of head-related transfer function

Methods for analyzing the spatial symmetry of head-related transfer function (HRTF) are proposed. The influences of anatomical structures on the symmetry of HRTF are investigated using HRTFs measured on KEMAR mannequin and human subjects. Results show that for KEMAR mannequin, pinnae destroy the front-back symmetry of HRTF above 5 to 6 kHz, while for human subjects the frequency reduces to 2.5 kHz because of the locations of ears. Furthermore, at low and median frequencies, HRTF is approximately left-right symmetrical. While as frequencies increase, the asymmetry caused by the fine anatomical leftright differences appears. The starting frequency and the extent of the left-right asymmetry in HRTF depend on individuals. The analyses demonstrate the spatial symmetrical characteristics of HRTF and the frequency ranges in which the current binaural models are valid.     

Perceptually based head-related transfer function database optimization

In the context of binaural audio rendering, choosing the best head-related transfer function (HRTF) for an individual from large databases poses several problems. This study proposes a method to reduce the size of a given HRTF database. Participants, 45 in total, were asked to rate the quality of binaural synthesis for 46 HRTFs. The lack of reciprocity in the ratings was noted. Results were used to create a perceptually optimized HRTF subset which satisfied all participants' judgments. The subset was validated using localization tests on a separate group of subjects with results showing reduced errors when subjects were given their best choice, rather than their worst choice HRTF.     

Using beamforming and binaural synthesis for the psychoacoustical evaluation of target sources in noise

The potential of spherical-harmonics beamforming (SHB) techniques for the auralization of target sound sources in a background noise was investigated and contrasted with traditional head-related transfer function (HRTF)-based binaural synthesis. A scaling of SHB was theoretically derived to estimate the free-field pressure at the center of a spherical microphone array and verified by comparing simulated frequency response functions with directly measured ones. The results show that there is good agreement in the frequency range of interest. A listening experiment was conducted to evaluate the auralization method subjectively. A set of ten environmental and product sounds were processed for headphone presentation in three different ways: (1) binaural synthesis using dummy head measurements, (2) the same with background noise, and (3) SHB of the noisy condition in combination with binaural synthesis. Two levels of background noise (62, 72 dB SPL) were used and two independent groups of subjects (N=14) evaluated either the loudness or annoyance of the processed sounds. The results indicate that SHB almost entirely restored the loudness (or annoyance) of the target sounds to unmasked levels, even when presented with background noise, and thus may be a useful tool to psychoacoustically analyze composite sources.     

Spatial unmasking of nearby pure-tone targets in a simulated anechoic environment

Detection thresholds were measured for different spatial configurations of 500- and 1000-Hz pure-tone targets and broadband maskers. Sources were simulated using individually measured head-related transfer functions (HRTFs) for source positions varying in both azimuth and distance. For the spatial configurations tested, thresholds ranged over 50 dB, primarily as a result of large changes in the target-to-masker ratio (TMR) with changes in target and masker locations. Intersubject differences in both HRTFs and in binaural sensitivity were large; however, the overall pattern of results was similar across subjects. As expected, detection thresholds were generally smaller when the target and masker were separated in azimuth than when they were at the same location. However, in some cases, azimuthal separation of target and masker yielded little change or even a small increase in detection threshold. Significant intersubject differences occurred as a result both of differences in monaural and binaural acoustic cues in the individualized HRTFs and of different binaural contributions to performance. Model predictions captured general trends in the pattern of spatial unmasking. However, subject-specific model predictions did not account for the observed individual differences in performance, even after taking into account individual differences in HRTF measurements and overall binaural sensitivity. These results suggest that individuals differ not only in their overall sensitivity to binaural cues, but also in how their binaural sensitivity varies with the spatial position of (and interaural differences in) the masker.     

基于稀疏表示和特征加权的离格双耳声源定位*

基于头相关传递函数数据库的传统双耳声源定位方法的定位角度往往被限定在头相关传递函数数据库的离散测量点上。当头相关传递函数数据库的测量方位角间隔较大时,这类算法的性能会显著下降,这就是典型的离格问题。该文提出了基于加权宽带稀疏贝叶斯学习的离格双耳声源定位算法。首先该算法建立离格双耳信号的稀疏表示模型,然后利用双耳相干与扩散能量比特征对各个频点进行加权以降低噪声和混响的影响,最后通过加权宽带稀疏贝叶斯学习方法估计离格声源的方位角。实验结果表明,该算法在各种复杂的声学环境下都有着较高的定位精度和鲁棒性,特别是提高了离格条件下的声源定位性能。     

近场头相关传输函数的测量与分析

设计了测量距离可调整的头相关传输函数的实验测量方法，并采用人工头进行近场头相关传输函数的测量，建立了高空间分辨率的近场头相关传输函数数据库，为进一步开展双耳听觉的研究和虚拟听觉的应用提供了数据基础。根据实验数据，初步分析了远、近场情况下，距离、仰角、方位角等参量对头相关传输函数的影响规律。     

Design and validation on a multiple sound source fast-measurement system of near-field head-related transfer functions

Near-field head-related transfer functions(HRTFs) are essential to scientific researches of binaural hearing and practical applications of virtual auditory display. High efficiency, accuracy and repeatability are required in a near-field HRTF measurement. Hence,there is no reference which intents on solving the measuring difficulties of near-field HRTF for human subjects. In present work, an efficient near-field HRTF measurement system based on computer control is designed and implemented, and a fast calibration method for the system is proposed to first solve the measurement of near-field HRTF for human subjects. The efficiency of measurement is enhanced by a comprehensive design on the acoustic, electronic and mechanical parts of the system. And the accuracy and repeatability of the measurement are greatly improved by carefully calibrating the positions of sound source, subject and binaural microphones.This system is suitable for near-field HRTF measurement at various source distances within 1.0 m, for both human subject and artificial head. The time costs of HRTF measurement at a single sound source distance and full directions has been reduced to less than 20 minutes. The measurement results indicate that the accuracy of the system satisfies the actual requirements.The system is applicable to scientific research and can be used to establish an individualized near-field HRTF database for human subjects.     

Recovery of individual head-related transfer functions from a small set of measurements

Head-related transfer functions (HRTFs) vary with individuals, and in practice, measuring HRTFs with high directional resolution for each individual is tiresome. Based on a basis functions representation of HRTFs, the present work proposes a method for recovering individual HRTFs from a small set of measurements. The HRTFs are represented by a combination of a small set of spatial basis functions (SBFs) with frequency- and individual-dependent weights. The SBFs are derived by applying spatial principal component analysis to a baseline HRTF dataset with high directional resolution. The individual weights for any subject outside the dataset are estimated from measurements at a few source directions, and then the HRTFs with high directional resolution are recovered by combining the SBFs and the individual weights. In an illustrative case, the SBFs derived from a baseline dataset that includes 20 subjects are used to recover the HRTF magnitudes for six subjects outside the baseline dataset. Results show that individual HRTF magnitudes can be recovered from measurements at 73 directions with a mean signal-to-distortion ratio of 19 dB. The proposed method is also applicable to recovering head-related impulse responses. The results of psychoacoustic experiments indicate that in most cases the recovered and measured HRTFs are indistinguishable.