Does a single zealot affect an infinite group of voters?

A method for studying the exact properties of a class of inhomogeneous stochastic many-body systems is developed and presented in the framework of a voter model perturbed by the presence of a "zealot," an individual allowed to favor an "opinion." We compute exactly the magnetization of this model and find that in one (1D) and two dimensions (2D) it evolves, algebraically ( approximately t(-1/2)) in 1D and much slower ( approximately 1/ln(t) in 2D, towards the unanimity state chosen by the zealot. In higher dimensions the stationary magnetization is no longer uniform: the zealot cannot influence all the individuals. The implications to other physical problems are also pointed out.     

The pursuit of invariance in speech signals

The search for the acoustic properties useful to the listener in extracting the linguistic message from a speech signal is often construed as the task of matching invariant physical properties to invariant phonological percepts; the discovery of the former will explain the latter. These phonological percepts are essentially the phonemes of pregenerative phonology, and they are more or less faithfully reflected in standard alphabetic writing. Thus English deep and doom are supposed to be perceptually identical in their initial /d/s; the orthographic similarity is in agreement with the linguist's "representation" of these forms. The partial identity in spelling is only weak evidence for perceptual invariance, however. First, while some phonemes may comprise a single "sound," others are said by linguists to include phonetically distinct ones. Thus English /p/includes both aspirated and unaspirated voiceless labial stops. The view that it is not the phoneme, but rather the phonetic feature, to which an acoustic invariant might be attributed, raises two questions: (a) Since segments sharing a feature are rarely judged to constitute a single sound, the search for a feature-specific invariant, whose function is to explain perceptual constancy, is deprived of its essential motivation, and (2) there is no more reason to expect the acoustic cues to a feature to be context-independent than is the case with the phoneme. What seems more likely is to find that some phonemes, and some features, are more invariantly marked in the speech signal than others.     

A note on the modal kurtosis and the concentration factor in reverberation rooms

The effect known as "weak Anderson localization," "coherent backscattering," or "enhanced back-scattering" is a physical phenomenon that occurs in random systems, e.g., disordered media and linear wave systems, including reverberation rooms: The mean square response is increased at the drive point. In a reverberation room, this means that one can expect an increase of the reverberant sound field at the position of the source that generates the sound field. This affects the sound power output of the source and is therefore of practical concern. The relative increase of reverberant energy is described by the concentration factor, which is usually assumed to be 2. However, because of the stronger direct sound field at the source position, it is obviously very difficult to measure this quantity directly under steady-state conditions. A related parameter of crucial importance for the ensemble statistics of responses in rooms is the modal kurtosis, which is usually assumed to be 3. The modal kurtosis is also very difficult to measure directly. This paper presents the results of an indirect experimental estimation of the two parameters.     

Characterizing the sound quality of air-conditioning noise

The aim of the psychoacoustic study presented here was to characterize listeners' preferences for a set of sounds produced by different brands and models of indoor air-conditioning units. In addition, some synthetic sounds, created by interpolation between recorded sound samples, were integrated into the set. The multidimensional perceptual space and the corresponding physical space representative of the sound set were determined with multidimensional scaling (MDS). Then the preferences for different classes of listeners were related to the physical space. The best spatial model yielded by the MDS had three common dimensions and specificities. The three dimensions are correlated with the ratio of the noisy part of the spectrum to the harmonic part (NHR), with the spectral center of gravity (SC) and with loudness (N). Two classes of listeners can be distinguished in terms of preference. For one, preference varied primarily with loudness, whereas for the other it varied more with SC and NHR. However, for one class the preference grew with the parameter NHR, while it decreased for the other class. The results replicate under different laboratory conditions and indicate the usefulness of this sound quality assessment approach for characterizing appliance noises.     

The psychomechanics of simulated sound sources: material properties of impacted bars

Sound can convey information about the materials composing an object that are often not directly available to the visual system. Material and geometric properties of synthesized impacted bars with a tube resonator were varied, their perceptual structure was inferred from multidimensional scaling of dissimilarity judgments, and the psychophysical relations between the two were quantified. Constant cross-section bars varying in mass density and viscoelastic damping coefficient were synthesized with a physical model in experiment 1. A two-dimensional perceptual space resulted, and the dimensions were correlated with the mechanical parameters after applying a power-law transformation. Variable cross-section bars varying in length and viscoelastic damping coefficient were synthesized in experiment 2 with two sets of lengths creating high- and low-pitched bars. In the low-pitched bars, there was a coupling between the bar and the resonator that modified the decay characteristics. Perceptual dimensions again corresponded to the mechanical parameters. A set of potential temporal, spectral, and spectrotemporal correlates of the auditory representation were derived from the signal. The dimensions related to mass density and bar length were correlated with the frequency of the lowest partial and are related to pitch perception. The correlate most likely to represent the viscoelastic damping coefficient across all three stimulus sets is a linear combination of a decay constant derived from the temporal envelope and the spectral center of gravity derived from a cochlear representation of the signal. These results attest to the perceptual salience of energy-loss phenomena in sound source behavior.     

Communicative Suitability of Voice Following Radiotherapy for T1 Glottic Carcinoma: Testing the Reliability of a Rating Instrument

The objective of the study was to determine whether a communicative suitability rating instrument could be used in a meaningful way to assess functionality of voice following radiotherapy for T1 glottic cancer. Seventeen naive listeners judged the suitability of voice of a patient group with T1 glottic carcinoma (n = 20) just before treatment, a group of patients (n = 40) after radiotherapy, and a matched control group (n = 20) of normal speakers. Listeners rated suitability on a 10-point scale for 10 speaking situations, which supposedly make different demands. In order to validate scores on communicative suitability, ratings were related to perceptual voice quality evaluations and videolaryngostroboscopic evaluations. Results indicate that the concept of measuring listener judgments of communicative suitability of voice is basically sound. Raters are reliable and can discriminate between groups of normal and pathological voices. Patients with T1 glottic carcinoma (assessed before the start of treatment) have on average the least suitable voices. Following radiotherapy suitability is, on average, improved, but does not approach the suitability of normal voices. Ratings on communicative suitability were clearly related to perceptual voice quality aspects and videolaryngostroboscopic evaluations. A subset of three communicative suitability rating scales is recommended as part of the protocol for evaluating voice outcome after radiotherapy for early glottic cancer, besides perceptual evaluation of voice quality by trained and naive raters, videolaryngostroboscopy, acoustical analyses, and self-ratings of vocal performance.     

Perceived sound quality of reproductions with different frequency responses and sound levels

Three programs (female voice, jazz music, and pink noise) were reproduced using four different frequency responses and two different sound levels. Fourteen normal hearing subjects listened to the reproduction via earphones and judged the sound quality on seven perceptual scales (loudness, clarity, fullness, spaciousness, brightness, softness/gentleness, and nearness) and a fidelity scale. Significant differences among the reproductions appeared in all scales and could be attributed to the differences in frequency response or sound level or both. Interactions between the reproductions and the programs could be explained by the relations between the spectrum of the programs and the frequency responses used. The results for the noise program were similar to those for the jazz music program.     

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。     

The acoustic bases for gender identification from children's voices.

The purpose of this study was to examine the acoustic characteristics of children's speech and voices that account for listeners' ability to identify gender. In Experiment I, vocal recordings and gross physical measurements of 4-, 8-, 12-, and 16-year olds were taken (10 girls and 10 boys per age group). The speech sample consisted of seven nondiphthongal vowels of American English (/ae/ "had," /E/ "head," /i/ "heed," /I/ "hid," /a/ "hod," /inverted v/ "hud," and /u/ "who'd") produced in the carrier phrase, "Say /hVd/ again." Fundamental frequency (f0) and formant frequencies (F1, F2, F3) were measured from these syllables. In Experiment II, 20 adults rated the syllables produced by the children in Experiment I based on a six-point gender rating scale. The results from these experiments indicate (1) vowel formant frequencies differentiate gender for children as young as four years of age, while formant frequencies and f0 differentiate gender after 12 years of age, (2) the relationship between gross measures of physical size and vocal characteristics is apparent for at least 12- and 16-year olds, and (3) listeners can identify gender from the speech and voice of children as young as four years of age, and with respect to young children, listeners appear to base their gender ratings on vowel formant frequencies. The findings are discussed in relation to the development of gender identity and its perceptual representation in speech and voice.     

Frustration and sound attenuation in structural glasses

Three classes of harmonic disorder systems (Lennard-Jones-like glasses, percolators above threshold, and spring disordered lattices) have been numerically investigated in order to clarify the effect of different types of disorder on the mechanism of high frequency sound attenuation. We introduce the concept of frustration in structural glasses as a measure of the internal stress, and find a strong correlation between the degree of frustration and the exponent alpha that characterizes the momentum dependence of the sound attenuation gamma(Q) approximately Qalpha. In particular, alpha decreases from approximately d+1 in low-frustration systems (where d is the spectral dimension) to approximately 2 for high-frustration systems such as the realistic glasses examined.     

The sound level of the singer's formant in professional singing

The relative sound level of the "singer's formant," measured in a 1/3-oct band with a center frequency of 2.5 kHz for males and of 3.16 kHz for females, has been investigated for 14 professional singers, nine different modes of singing, nine different vowels, variations in overall sound-pressure level, and fundamental frequencies ranging from 98 up to 880 Hz. Variation in the sound level of the singer's formant due to differences among male singers was small (4 dB), the factors vowels (16 dB) and fundamental frequency (9-14 dB) had an intermediate effect, while the largest variation was found for differences among female singers (24 dB), between modes of singing (vocal effort) (23 dB), and in overall sound-pressure level (more than 30 dB). In spite of this great potential variability, for each mode of singing the sound level of the singer's formant was remarkably constant up to F0 = 392 Hz, due to adaptation of vocal effort. This may be explained as the result of the perceptual demand of a constant voice quality. The definition of the singer's formant is discussed.     

Perceptual evaluation of multi-dimensional spatial audio reproduction

Perceptual differences between sound reproduction systems with multiple spatial dimensions have been investigated. Two blind studies were performed using system configurations involving 1-D, 2-D, and 3-D loudspeaker arrays. Various types of source material were used, ranging from urban soundscapes to musical passages. Experiment I consisted in collecting subjects' perceptions in a free-response format to identify relevant criteria for multi-dimensional spatial sound reproduction of complex auditory scenes by means of linguistic analysis. Experiment II utilized both free response and scale judgments for seven parameters derived form Experiment I. Results indicated a strong correlation between the source material (sound scene) and the subjective evaluation of the parameters, making the notion of an "optimal" reproduction method difficult for arbitrary source material.     

Speech interference in food courts of shopping centres

The acoustics of food courts were investigated. Maximum A-weighted sound pressure levels (SPLs) were defined, based on studies of quality of communication among people in noisy places. A survey in twelve food courts was carried out and two case studies were selected, which presented poor quality of communication. An analytical formula to evaluate the SPL was employed and good agreement was obtained between these evaluations and in situ measurements. However, further studies would be necessary to confirm the applicability of the analytical procedure since it was assumed in the calculations that the sound field was diffuse. Noise from other sources apart from speech significantly affected the SPL and it appears that this is the main aspect to be tackled in the acoustical design. Potential improvements on the acoustics of these enclosures were investigated. Several arrangements of absorbent materials were considered and application on the ceiling was generally the best option.     

The relationship between the cross-correlation coefficient of two-channel acoustic signals and sound image quality

In order to investigate sound image quality, white and bandlimited noises with various cross-correlation coefficients are reproduced from two loudspeakers placed in anechoic or echoic chambers. Subjects are asked to make similarity judgments and some subjective evaluations of pairs of the noises. The experimental data are analyzed by Kruskal's multidimensional scaling (MDS) program. The analysis of the experimental data shows the following: (1) sound image quality depends mostly on the width and the distance of the sound image, (2) the width of the sound image depends on the absolute value of the cross-correlation coefficient, (3) the distance of the sound image depends on the cross-correlation coefficient itself, (4) with respect to physical and psychological factors governing sound image quality, there is no fundamental difference between anechoic and echoic chambers.     

Perceptual relevance of the temporal envelope to the speech signal in the 4-7 kHz band

The perceptual relevance of adopting the temporal envelope to model the frequency band of 4-7 kHz (highband) in wideband speech signal is described in this letter. Based on theoretical work in psychoacoustics, we find out that the temporal envelope can indeed be a perceptual cue for the high-band signal, i.e., a noiseless sound can be obtained if the temporal envelope is roughly preserved. Subjective listening tests verify that transparent quality can be obtained if the model is used for the 4.5-7 kHz band. The proposed model has the benefits of offering flexible scalability and reducing the cost for quantization in coding applications.     

Non-isomorphism in efficient coding of complex sound properties

To the extent that sensorineural systems are efficient, stimulus redundancy should be captured in ways that optimize information transmission. Consistent with this principle, neural representations of sounds have been proposed to become "non-isomorphic," increasingly abstract and decreasingly resembling the original (redundant) input. Here, non-isomorphism is tested in perceptual learning using AXB discrimination of novel sounds with two highly correlated complex acoustic properties and a randomly varying third dimension. Discrimination of sounds obeying the correlation became superior to that of sounds violating it despite widely varying physical acoustic properties, suggesting non-isomorphic representation of stimulus redundancy.     

Illusory spectrotemporal ripples created with binaurally correlated noise

Binaural disparities are the primary acoustic cues employed in sound localization tasks. However, the degree of binaural correlation in a sound serves as a complementary cue for detecting competing sound sources [J. F. Culling, H. S. Colburn, and M. Spurchise, "Interaural correlation sensitivity," J. Acoust. Soc. Am. 110(2), 1020-1029 (2001) and L. R. Bernstein and C. Trahiotis, "On the use of the normalized correlation as an index of interaural envelope correlation," J. Acoust. Soc. Am. 100, 1754-1763 (1996)]. Here a random chord stereogram (RCS) sound is developed that produces a salient pop-out illusion of a slowly varying ripple sound [T. Chi et al., "Spectro-temporal modulation transfer functions and speech intelligibility," J. Acoust. Soc. Am. 106(5), 2719-2732 (1999)], even though the left and right ear sounds alone consist of noise-like random modulations. The quality and resolution of this percept is systematically controlled by adjusting the spectrotemporal correlation pattern between the left and right sounds. The prominence and limited time-frequency resolution for resolving the RCS suggests that envelope correlations are a dominant binaural cue for grouping acoustic objects.