Use of autocorrelation analysis to characterize audibility of low-frequency tonal signals

Autocorrelation function (ACF) parameters were used to identify low-frequency tonal sound detected in actual living environments. Five houses whose residents had made complaints for unidentified noise were selected as measurement sites. The sounds and the residents' detection responses were recorded simultaneously inside a room in each house. When they heard the suspected noise, the participants pushed a response button on a portable recording device as the sound was recorded. Results showed that tonal components in the low-frequency range were highly correlated with the sound detection. This study suggests that autocorrelation analysis can reveal the human detection of low-frequency tonal signals. Low-frequency tonal components were identified and quantified using ACF parameters: the delay time and amplitude of the ACF's first dominant peak. The amplitude was useful to describe the detection and prominence of low-frequency tonal components in noise.     

Recognizing transient low-frequency whale sounds by spectrogram correlation

A method is described for the automatic recognition of transient animal sounds. Automatic recognition can be used in wild animal research, including studies of behavior, population, and impact of anthropogenic noise. The method described here, spectrogram correlation, is well-suited to recognition of animal sounds consisting of tones and frequency sweeps. For a sound type of interest, a two-dimensional synthetic kernel is constructed and cross-correlated with a spectrogram of a recording, producing a recognition function--the likelihood at each point in time that the sound type was present. A threshold is applied to this function to obtain discrete detection events, instants at which the sound type of interest was likely to be present. An extension of this method handles the temporal variation commonly present in animal sounds. Spectrogram correlation was compared to three other methods that have been used for automatic call recognition: matched filters, neural networks, and hidden Markov models. The test data set consisted of bowhead whale (Balaena mysticetus) end notes from songs recorded in Alaska in 1986 and 1988. The method had a success rate of about 97.5% on this problem, and the comparison indicated that it could be especially useful for detecting a call type when relatively few (5-200) instances of the call type are known.     

首次测到引力波

100年前爱因斯坦广义相对论预言引力波。它可形象地看作弯曲时空中的涟漪;天体物理过程越激烈,引力波辐射越强。当引力波传播时,时空将在垂直于传播方向挤压和拉伸。一般要发现这种极其微小的变化是非常困难的。LIGO 干涉仪臂长4 km;2015年升级改造后非常灵敏,能够检测到比原子核尺寸小得多的臂长变化。通过分析LIGO记录到的数据,美国和欧洲的科学家们推断：已经成功探测到两个黑洞合并产生的引力波。这一对黑洞距地球约13 亿光年;并合前约为太阳质量的36和29倍,并合后形成一个约62倍太阳质量黑洞。     

GS方法恢复低频相位噪声

 将Gerchberg-Saxton(GS)反演方法应用于恢复高功率激光装置的低频相位噪声研究中,通过数值模拟计算,给出了很好的迭代结果。为设计合理的相位板提供了依据。同时也为光束诊断系统提供了一种测量相位的方法。     

GS方法恢复低频相位噪声

将Gerchberg-Saxton(GS)反演方法应用于恢复高功率激光装置的低频相位噪声研究中,通过数值模拟计算,给出了很好的迭代结果。为设计合理的相位板提供了依据。同时也为光束诊断系统提供了一种测量相位的方法。     

Intrusive sounds

The aim of this paper is to propose measures of intrusiveness of sound. Intrusiveness is understood here as that feature of sound which determines a high degree of annoyance in spite of the low value of noise rating. The paper discusses existing noise ratings and shows that they do not give satisfactory results as applied to sounds estimated as irritating or unpleasant. It is proposed that noise ratings should be extended to cover measures of intrusiveness.     

The effect of low-frequency oscillations on cardio-respiratory synchronization

We show that the transitions which occur between close orders of synchronization in the cardiorespiratory system are mainly due to modulation of the cardiac and respiratory processes by low-frequency components. The experimental evidence is derived from recordings on healthy subjects at rest and during exercise. Exercise acts as a perturbation of the system that alters the mean cardiac and respiratory frequencies and changes the amount of their modulation by low-frequency oscillations. The conclusion is supported by numerical evidence based on a model of phase-coupled oscillators, with white noise and lowfrequency noise. Both the experimental and numerical approaches confirm that low-frequency oscillations play a significant role in the transitional behavior between close orders of synchronization.     

低频宽带大功率“星型”柱面发射换能器

提出一种具有水平无指向性、低频、宽带、大功率特点的新结构换能器——“星型”柱面发射换能器,换能器由共享后质量块的6个复合棒换能器按“星型”方式组成柱面结构。采用有限元方法对换能器进行了分析设计并制作了换能器样机。在1—10 kHz内,换能器有3个主要工作模态,前两阶工作模态对换能器工作带宽的展宽有贡献,第三阶模态显示出较强的指向性,水池测试换能器具有1倍频程的工作带宽,最大声源级为199.1 dB。有限元模拟结果和实验结果符合较好。研究结果表明,新结构换能器在满足水平无指向性的前提下,利用复合棒的纵振及辐射面的弯曲振动实现了低频、宽带、大功率的要求,提供了一种设计该特性换能器的新思路。     

The low-frequency sound speed of fluid-like gas-bearing sediments

The low-frequency sound speed in a fluid-like kaolinite sediment containing air bubbles was measured using an acoustic resonator technique and found to be 114 ms with negligible dispersion between 100 and 400 Hz. The sediment's void fraction and bubble size distribution was determined from volumetric images obtained from x-ray computed tomography scans. A simplified version of Wood's effective medium model, which is dependent only upon the ambient pressure, the void fraction, the sediment's bulk mass density, and the assumption that all the bubbles are smaller than resonance size at the highest frequency of interest, described the measured sound speed.     

低频用周期性结构管道的研究

在扬声器单元的一侧耦合管道是解决声短路,实现低频下潜的有效方法。本文研究了一种周期性结构管道,对其低频辐射特性进行理论分析,提出了使用周期性结构管道代替传统均匀管道以缩短长度。在实际的扬声器单元上分别耦合传统的均匀管道和周期性结构管道,实验结果与理论计算基本吻合。结果表明,为实现相同的低频下潜,合理的周期性结构可以有效地缩短管道长度,从而具有更高的实用价值。     

Theory of heart sounds

A phenomenological theory of heart sounds is proposed. The left ventricular wall is modelled as an incompressible spherical shell and the heart valves as two-dimensional membranes. The solutions of the appropriate elasticity equations are matched with those of the hydrodynamical equations describing the propagation of the radiated sound through the soft body tissue. The predicted time plots and frequency spectra show significant resemblance with recorded ones, like equidistant peaks, directional dependence, relationship of sound amplitude and rate of pressure change inside the left ventricle, etc. Sets of parameters are singled out which influence the measured sound. The latter is the integral part of a diagnostic procedure.     

The processing and perception of size information in speech sounds

There is information in speech sounds about the length of the vocal tract; specifically, as a child grows, the resonators in the vocal tract grow and the formant frequencies of the vowels decrease. It has been hypothesized that the auditory system applies a scale transform to all sounds to segregate size information from resonator shape information, and thereby enhance both size perception and speech recognition [Irino and Patterson, Speech Commun. 36, 181-203 (2002)]. This paper describes size discrimination experiments and vowel recognition experiments designed to provide evidence for an auditory scaling mechanism. Vowels were scaled to represent people with vocal tracts much longer and shorter than normal, and with pitches much higher and lower than normal. The results of the discrimination experiments show that listeners can make fine judgments about the relative size of speakers, and they can do so for vowels scaled well beyond the normal range. Similarly, the recognition experiments show good performance for vowels in the normal range, and for vowels scaled well beyond the normal range of experience. Together, the experiments support the hypothesis that the auditory system automatically normalizes for the size information in communication sounds.