Some insight into the acoustics of the didjeridu

The Australian didjeridu is a unique and interesting instrument. Despite the fact that the bore shape is almost random in nature and varies considerably across different instruments, the didjeridu timbre is readily recognizable. This is also true despite the fact that the player can manipulate the timbre more than in most wind instruments, by changing the shape of his vocal tract. In this study we examine the didjeridu spectrum in detail, in order to determine the characteristics that are similar across different instruments, those that are constant for a given instrument, and those that are readily influenced by the player. To this end we recorded and analyzed the sounds of eight instruments of different quality, all of them played across a range of timbres. Examining the resultant spectra, along with the resonance frequencies of these instruments, leads to a number of interesting conclusions. One of these is that the random nature of the instrument bore is actually conducive to creating its typical timbre. We also give a preliminary explanation of the differences between good and poor instruments.     

传统笙的物理模型及声音合成方法

为研究传统笙的物理结构与音色之间的关系,提出了传统笙的物理模型及声音合成方法。在簧舌振动模型的基础上,结合指孔和音窗的传输矩阵计算方法,建立了笙管的等效电路,并将二者结合,得到笙的完整物理模型。为了验证模型的有效性,设计了一套笙的实验系统,实现了对笙管发声过程中特征量的多通道同步测量。通过对比实验和模型仿真结果的时频域特点以及与音色相关的特征量,分析了模型的性能.结果表明,该模型可较好地模拟传统笙管的发声过程,合成笙样本能够较准确的反映真实笙样本的音色特征。      

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。      

Analysis with binaural auditory model and experiment on the timbre of Ambisonics recording and reproduction

A scheme for analyzing the timbre in spatial sound with binaural auditory model is proposed and the Ambisonics is taken as an example for analysis.Ambisonics is a spatial sound system based on physical sound field reconstruction.The errors and timbre colorations in the final reconstructed sound field depend on the spatial aliasing errors on both the recording and reproducing stages of Ambisonics.The binaural loudness level spectra in Ambisonics reconstruction is calculated by using Moore's revised loudness model and then compared with the result of real sound source,so as to evaluate the timbre coloration in Ambisonics quantitatively.The results indicate that,in the case of ideal independent signals,the high-frequency limit and radius of region without perceived timbre coloration increase with the order of Ambisonics.On the other hand,in the case of recording by microphone array,once the high-frequency limit of microphone array exceeds that of sound field reconstruction,array recording influences little on the binaural loudness level spectra and thus timbre in final reconstruction up to the highfrequency limit of reproduction.Based on the binaural auditory model analysis,a scheme for optimizing design of Ambisonics recording and reproduction is also suggested.The subjective experiment yields consistent results with those of binaural model,thus verifies the effectiveness of the model analysis.     

The admittance feature representation and impact sound feature extraction in the material identification of ribbed plates

The admittance features representing the physical attributes are used as the intermediates to extract the material-attributes-related impact sound features of ribbed plates.Firstly, the admittance feature representations of metal ribbed plates attributes are obtained and the relationship between the admittance features and the impact sound features are established via correlation analysis method. Then, material-attributes-related impact sound features are obtained indirectly. Finally, the performances of different sound features for the material recognition of ribbed-metal plates are verified through the Support Vector Machine classifier.The results indicate that the obtained four sets of features can effectively identify the materials of the metal ribbed plates, while the accuracy of a single feature depends on the separable degree of the corresponding material attribute. And the features extracted based on admittance functions have higher average accuracy than that of timbre features. Therefore, the proposed sound feature extraction method based on admittance features is valid, and the extracted sound features can effectively reflect the physical attributes.     

加筋板材料辨识的导纳特征表达与冲击声特征提取

以表征物理属性的导纳特征为中间量,提取与加筋板材料属性有关的冲击声特征。先用相关分析方法获得金属加筋板物理属性的导纳特征表达以及导纳特征与冲击声特征之间的联系,间接得到表征声源物理属性的冲击声特征,然后通过支持向量机分类器验证不同特征在金属加筋板材料分类辨识中的性能。结果表明,所得的4组冲击声特征能准确识别出不同的材料,单个特征的识别率与对应材料属性的可分程度有关,理想冲击声声特征比音色特征的平均识别率更高。由此可见,利用导纳特征提取与材料属性相关冲击声特征的方法是有效的,且所提的特征能够很好的反映声源材料属性。      

Influence of the Number of Loudspeakers on the Timbre in Horizontal and Mixed-Order Ambisoncis Reproduction

Ambisonics is a series of flexible spatial sound reproduction systems based on spatial harmonics decomposition of sound field. Traditional horizontal and spatial Ambisonics reconstruct horizontal and spatial sound field with certain order of spatial harmonics, respectively. Both the Shannon-Nyquist spatial sampling frequency limit for accurately reconstructing sound field and the complexity of system increase with the increasing order of Ambisonics. Based on the fact that the horizontal localization resolution of human hearing is higher than vertical resolution, mixed-order Ambisonics (MOA) reconstructs horizontal sound field with higher order spatial harmonics, while reconstructs vertical sound field with lower order spatial harmonics, and thereby reaches a compromise between the perceptual performance and the complexity of system. For a given order horizontal Ambisoncis or MOA reproduction, the number of horizontal loudspeakers is flexible, providing that it exceeds some low limit. By using Moore’s revised loudness model, the present work analyzes the influence of the number of horizontal loudspeakers on timbre both in horizontal Ambisonics and MOA reproduction. The binaural loudness level spectra (BLLS) of Ambisoncis reproduction are calculated and then compared with those of target sound field. The results indicate that below the Shannon-Nyquist limit of spatial sampling, increasing the number of horizontal loudspeakers influence little on BLLS then timbre. Above the limit, however, the BLLS for Ambisoncis reproduction deviate from those of target sound field. The extent of deviation depends on both the direction of target sound field and the number of loudspeakers. Increasing the number of horizontal loudspeakers may increase the change of BLLS then timbre in some cases, but reduce the change in some other cases. For MOA, the influence of the number of horizontal loudspeakers on BLLS and timbre reduces when virtual source departs from horizontal plane to the high or low elevation. The subjective evaluation experiment also validates the analysis.     

The metre

A musical wind instrument transforms a constant pressure input from the player's mouth into a fluctuating pressure output in the form of a radiating sound wave. In reed woodwind and brass instruments, this transformation is achieved through a nonlinear coupling between two vibrating systems: the flow control valve formed by the mechanical reed or the lips of the player, and the air column contained by the pipe. Although the basic physics of reed wind instruments was developed by Helmholtz in the nineteenth century, the application of ideas from the modern theory of nonlinear dynamics has led to recent advances in our understanding of some musically important features of wind instrument behaviour. As a first step, the nonlinear aspects of the musical oscillator can be considered to be concentrated in the flow control valve; the air column can be treated as a linear vibrating system, with a set of natural modes of vibration corresponding to the standing waves in the pipe. Recent models based on these assumptions have had reasonable success in predicting the threshold blowing pressure and sounding frequency of a clarinet, as well as explaining at least qualitatively the way in which the timbre of the sound varies with blowing pressure. The situation is more complicated for brass instruments, in which the player's lips provide the flow valve. Experiments using artificial lips have been important in permitting systematic studies of the coupling between lips and air column; the detailed nature of this coupling is still not fully understood. In addition, the assumption of linearity in the air column vibratory system sometimes breaks down for brass instruments. Nonlinear effects in the propagation of high amplitude sound waves can lead to the development of shock waves in trumpets and trombones, with important musical consequences.     

水下噪声音色属性回归模型及其在目标识别中的应用

通过对声音的主观评价与客观分析而建立的主观感受数学模型,在许多领域都有重要的应用. 本文采用多元线性回归分析手段对水下噪声音色属性建立回归模型,提取音色特征并改善水下目标的识别效果. 首先,在前期水下噪声音色属性主观评价实验的基础上,将构成音色属性空间的5个成分的评价分值作为回归分析中的因变量,提取大量与听觉感知相关的听觉特征作为自变量;然后,通过相关分析和改进的逐步筛选法,挑选出反映音色属性的“最优”自变量子集;最后,利用向后剔除回归分析和水下目标识别实验,确定适当的音色模型,并通过假设检验证明该线性模型不仅正确有效,而且能改善水下目标识别效果. 关键词： 音色 多元线性回归 主观评价     

水下噪声音色属性回归模型及其在目标识别中的应用

通过对声音的主观评价与客观分析而建立的主观感受数学模型,在许多领域都有重要的应用. 本文采用多元线性回归分析手段对水下噪声音色属性建立回归模型,提取音色特征并改善水下目标的识别效果. 首先,在前期水下噪声音色属性主观评价实验的基础上,将构成音色属性空间的5个成分的评价分值作为回归分析中的因变量,提取大量与听觉感知相关的听觉特征作为自变量;然后,通过相关分析和改进的逐步筛选法,挑选出反映音色属性的“最优”自变量子集;最后,利用向后剔除回归分析和水下目标识别实验,确定适当的音色模型,并通过假设检验证明该线性模型不仅正确有效,而且能改善水下目标识别效果.     

点簧簧片振动特性数值分析

簧片是笙等中国传统簧管类乐器的核心部件之一.通过点簧工艺可调整簧片振动频率,点簧簧片的差异对整体乐器的声音效果具有重要影响.针对点簧簧片的振动特性问题,对其建立非均匀截面并具有质量负载的振动模型,采用有限元方法计算点簧簧片的固有频率.大量算例分析了点簧质量、位置以及簧片的边界条件对振动频率的影响,研究发现:若点簧质量不...     

Can listeners hear who is singing? A comparison of three-note and six-note discrimination tasks

Timbre is typically investigated as a perceptual attribute that differentiates a sound source at one pitch and loudness. Yet the perceptual usefulness of timbre is that it allows the listener to recognize one sound source at different pitches. This paper investigated the ability of listeners to identify which pitch in an ascending or descending sequence of three or six stimuli was sung by a different singer. For three-note sequences, the task was extremely difficult, and with rare exceptions, listeners chose the most dissimilarly pitched stimulus as coming from the oddball singer. For six-note sequences, the detection of the oddball singer was much improved in spite of the added complexity of the task. These results support the idea that timbre should be understood as a transformation that connects the different sounds of one source and that a "rich" set of sounds is necessary to discover the trajectory.     

笙的簧片物理参数与音色相关性的初步研究

为了改善笙的声音品质,本文研究了笙的簧片物理尺度与笙的音色之间的相关性。在提出笙的物理模型并验证其有效性的基础上,固定音高,改变簧舌的厚度、长度以及缝隙宽度,合成一组笙的声样本。通过对偶比较法以及多维尺度法分析笙的音色空间,根据簧舌参数及音色特征量解释该音色空间的物理意义,并从发声原理比较簧舌参数对音色的作用。结果表明,音高一定时,簧舌宽度对音色的作用可忽略,厚度(及长度)和缝隙宽度对音色的作用相似,但影响方式不同。改变簧舌物理参数所形成的二维音色空间与声音的对数起振时间、频谱丰富性以及频谱不规则度有关。起振特征与频谱丰富性特征存在共变关系,通过改变这两个特征,能够改变音色的明亮度和柔软度。     

Vibroacoustic characteristics of a gothic harp

The "gothic" style of harp was popular across most of Europe from the late medieval period to the Renaissance. These harps have a one-piece, longitudinally oriented hardwood soundboard, as opposed to the transverse-oriented bonded softwood structure on a modern instrument. In addition, the one-piece back is flexible, whereas the back of a modern instrument is a rigid molded shell. To study the gothic harp, one was constructed from plans created by the Boston Museum of Fine Arts from a late German model in their collection. The vibrational behaviors of the soundboard and soundbox were measured at various stages of construction. The completed instrument was subjected to modal analysis and radiativity measurements. The sound radiation is dominated by two breathing modes at 188 and 273 Hz, each with strong motion of the back, and modes around 350 Hz. Taken together, these modes function like the A0/T1 resonance pairs seen in the soundboxes of other instruments, and a comparison is made with the guitar. Also observed is that as the frequency increases, radiation is emitted from higher up the soundboard, and from higher soundholes. This feature has been observed in other harps, and is a consequence of the harp family's unique geometry.     

采用无耳壳头相关传输函数的虚拟声信号处理

本文提出采用无耳壳、封闭耳道的头相关传输函数（HRTF）进行虚拟声信号处理的方法。理论分析表明，在包含功率均衡的扬声器虚拟声信号处理中，采用无耳壳、封闭耳道的头相关传输函数可有效地减少信号处理函数的谷点，从而减少声重发的音色改变。心理声学的实验结果表明，新处理方法的声像定位与传统的带耳壳、耳道的HRTF处理无显著区别，但音色较后者有所改善。因而新的方法更适合实际的虚拟声信号处理应用。     

基于听觉中枢模型的水下噪声音色表达与特性分析

为建立水下噪声音色特征的定量表达以用于目标识别, 本文将主观评价实验获得的 4个本质音色维度得分与声音的听觉中枢响应建立联系, 得到音色的偏最小二乘回归模型, 并基于回归系数对每个维度进行物理分析. 为验证该方法的有效性, 本文提取大量音色描述符作为自变量进行对比, 结果表明听觉中枢模型预测能力有一定优势. 同时发现, 前 3个本质音色维度可分别由高频能量比例、谱平坦程度和时域连续性描述, 而第4 维度则无法与任何声学特征建立联系. 关键词： 本质音色 听觉中枢模型 偏最小二乘回归 音色描述符     

Spider silk violin strings with a unique packing structure generate a soft and profound timbre

We overcome the difficulties in pulling long draglines from spiders, twist bundles of dragline filaments, and succeed in preparing violin strings. The twisting is found to change the cross section shapes of filaments from circular to polygonal and to optimize the packing structure with no openings among filaments providing mechanically strong and elastic strings. The spider string signal peaks of overtones for the violin are relatively large at high frequencies, generating a soft and profound timbre. Such a preferable timbre is considered to be due to the unique polygonal packing structure which provides valuable knowledge for developing new types of materials.     

The subjective assessment of trombone quality

A number of subjective experiments designed not only to assess the tonal and playing qualities of trombones but also to aid the interpretation of objective data is described. Quantifying multi-dimensional quantities such as timbre or quality is usually attempted either by multi-dimensional scaling (MDS) or by semantic differential scaling (SDS) and the advantages and disadvantages of each for the present purpose are briefly reviewed. For both methods additional information is needed either (for SDS) to aid the selection of scales, or (for MDS) to interpret the final results of the computer analysis; in this study such information is available from the investigations of Edwards [1]. A preliminary experiment testing the ability of subjects to rate trombone timbre using SDS showed that the intersubject variance was very large but that the order of factors governing timbre is (i) instrument, (ii) player and (iii) mouthpiece. A second experiment shows that pitch and loudness have a much greater influence on listener's ratings than do player, mouthpiece of instrument. Players' attitudes tested in further experiments show that the task of discriminating instruments when extraneous cues are removed is very hard indeed for most players, but a very few can be of quite remarkable discriminatory ability using either SDS or MDS. Results from one such player indicate clearly that timbre is the predominant acoustic factor deciding discrimination.