bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of bolted items on modal analysis performed on a car body
Authors: Colomo Miguel , Pietrzyk Andrzej , Kropp Wolfgang
Published: May 2008

When performing Modal Analysis testing on a BIG (body-in-gray), some bolted items are included to better take into account their influence on body stiffness. However, their contribution to the stiffness is not relevant in the frequency range accessible for modal analysis (usually up to 70 Hz on a BIG). On the other hand, these bolted items increase the dispersion between results obtained for nominally identical test objects. The question which arises is whether the items should be included in the BIG definition to perform modal analysis and, in this case, which is their influence on the results? MIMO (multi-input-multi-output) measurements were carried out over three, nominally identical, Volvo S80 BIGs. Several configurations were measured for each BIG, starting from the complete body the bolted items were progressively removed. A version of LMS PolyMAX method was programmed by Matlab to analyze the measured data. Conclusions about bolted items influence are drawn based on the study of stabilization diagrams and modal parameters. The poles selection by the stabilization diagrams is one of PolyMAX method keys. The method understanding obtained from programming allows studying the ins and outs of poles selection. Polynomial order plays an important role in physical poles identification, especially for closely spaced modes. Results are shown to highlight its relevance.
Control of harmonic distortion in a motor driven subsonic acoustic source
Authors: Johnson Marty , Toso Alessandro , Blandea Vincent
Published: May 2008

This paper presents a comparison of active control strategies used to reduce the harmonic distortion of a motor driven subsonic source. The source consists of a DC motor that drives a pair of speaker diaphragms through a belt drive system which in turn drives a pair of passive radiators through an acoustic enclosure. The motor drive system is inherently nonlinear with significant losses in force at polarity changes. A number of control strategies were tested both theoretically and experimentally in order to determine the best strategy for linearizing the output from the speaker. The methodologies tested were: (i) an FXLMS based adaptive time domain controller using a linear plant model, (ii) an FXLMS based adaptive frequency domain harmonic controller using a linear plant model, (iii) an FXLMS based adaptive frequency domain harmonic controller using a nonlinear plant model and (iv) a simplex based adaptive frequency domain harmonic controller. The time domain system is shown to suffer from slow adaption rates for the higher harmonics, the model based FXLMS harmonic controllers were shown to suffer from the nonstationarity of the nonlinear plant and the simplex method was shown to provide good results while being robust to slow variations in the plant.
Active control of engine noise transmitted into cavities: simulation, experimental validation and sound quality assessment
Authors: De Oliveira Leopoldo P. , Sas Paul , Desmet Wim , Janssens Karl , Gajdatsy Peter , Van Der Auweraer Herman
Published: May 2008

Active control has been proposed as a possible solution to cope with low frequency noise reduction in vehicles. Active noise control systems tend to be designed with a target on the sound pressure level reduction. However, the perceived control efficiency for the occupants can be more accurately assessed if psychoacoustic metrics are taken into account. The aim of this paper is to evaluate, numerically and experimentally, the effect of a collocated velocity feedback controller on the sound quality of engine noise in a vehicle mockup. The simulation scheme is described and experimentally validated. The engine excitation is provided by a sound quality equivalent engine simulator, running on a real-time platform that delivers harmonic excitation in function of the driving condition. The controller performance is evaluated in terms of sound quality metrics such as specific loudness and roughness. As a result of the control action, loudness is significantly reduced and roughness slightly spread, with an overall improvement on the perceived engine sound.
Practical implementation of low-latency DSP for feedback control of sound in research contexts
Authors: Berdahl Edgar , Lee Nelson , Niemeyer Guenter , Smith Julius O.
Published: May 2008

Feedback control of sound requires low-latency signal processing. In addition, because the human range of hearing extends roughly from 20 Hz to 20 kHz, controller hardware must process signals with relatively large bandwidths in comparison with common control applications. Over the past decade, the appropriate embedded hardware has become a niche product, so its cost has actually increased. The open source community has developed an excellent alternative: a general-purpose computer runs Linux with the real- time application interface (RTAI). Open source drivers (see www.comedi.org) enable software to communicate efficiently with data acquisition cards. For the first time, we describe in detail from start to finish how to configure such a system. In particular, we explain how to run control code from user space while still disabling interrupts. We further explain how to reserve a processor for running only feedback control code. This configuration achieves less than one sample of total system delay at sampling rates as high as 50 kHz. Other processors remain free to run standard Linux programs, allowing researchers to control sound with calls to many generic software libraries. We present detailed measurements of system jitter for various configurations and provide an example open-source toolbox demonstrating all these aspects at http://ccrma.stanford.edu/̃eberdahl/Projects/TFCMI.
Improvement of acoustic transmission loss by active modal mass control
Authors: Lhuillier Vincent , Pezerat Charles , Chesne Simon , Gaudiller Luc
Published: May 2008

This paper deals with an alternative modal control approach to reduce the sound transmission through a structure excited by an acoustic wave. Active control enables to conserve the characteristics of lightness while improving acoustic performances. For light and small structures having small modal overlap, the "modal mass damping control" is proposed. The aim of this control is to modify the modal distribution of high radiation efficiency modes with modal virtual mass and modal virtual damping. The interest of this approach is that at low frequencies, the active virtual mass effects shift down eigen frequencies to less audible frequency range while reducing vibration amplitudes in a broad frequency range. The modal virtual mass control appears to be a good complement to a standard damping control which is exclusively efficient at resonances. In order to detail the concept of the proposed method, an application is presented on a double panel equipped with piezoelectric patches. The structure is excited by a distributive acoustic plane wave. Acoustic transmission loss factors of the simulated controlled and the non-controlled smart structure are shown and optimization is discussed.
Active noise control in light jet aircraft
Authors: Pabst Oliver , Kletschkowski Thomas , Sachau Delf
Published: May 2008

Active systems for noise reduction are especially of interest when considering applications in which low-frequency noise is a main source of disturbance and only limited amounts of installation space and payload are available. This makes the adaptation and implementation of such systems plausible in vehicles such as automobiles and aircraft where passive reduction methods are restricted. In order to achieve effective active control in these environments, aspects such as the control method and actuator- and sensor-type as well as positioning must be considered. The noise characteristics are often known beforehand or are easily accessible by measurement. Using this data, an upper bound for possible noise reduction may be determined, e.g., by means of linear prediction methods. A current research project is aimed at developing an audiosystem for the cabin area of a light jet aircraft which, at the same time, should also function as an effective noise reduction system in order to enhance the cabin comfort as well as the audio quality. Using data from a measurement flight in a typical light jet aircraft, limitations of active control are determined. Furthermore, the testbed, an acoustic mockup, is presented, currently beholding a multichannel ANC- Audio system for tonal and broadband noise.
An hybrid method for sound transmission inside trains
Authors: Jean Philippe A. , Villot Michel
Published: May 2008

Hybrid methods mixing ray-tracing and energy approaches have been implemented and validated in the case of sound transmission inside a train. Generally, validation is proposed against measurements where it may be difficult to assess precisely the importance of the various assumptions and simplifications. In this paper, the proposed hybrid approach is compared to more precise numerical computations based on BEM and analytic models. This allows studying the importance of assumptions made on the computations of incident power and transmitted power. The case of a train in a tunnel has also been analysed where the sound field in the tunnel is computed by means of 2.5D BEM.
Critical assessment of operational path analysis: effect of coupling between path inputs
Authors: Gajdatsy Peter , Janssens Karl , Gielen Ludo , Mas Peter , Van Der Auweraer Herman
Published: May 2008

Classical transfer path analysis (TPA) is a widely used and reliable method for tackling noise and vibration problems. But due to its complexity and time-consuming procedure the industry is constantly seeking for simpler and faster methods. One such method, often referred to as operational path analysis (OPA), was presented in 2006 and has quickly gained popularity in the NVH field. The method works with measured operational input and output accelerations and sound pressures and the transmissibilities calculated from these. The claim for its accuracy is based on being able to reproduce the original output signal by summing the calculated partial contributions but it has not yet been compared to other TPA methods. This new method is now critically examined and compared to a reliable classical TPA measurement. The results of this examination reveal three significant weaknesses. This paper deals with the effect of the cross-coupling between the input signals. Due to modal behavior a single force will cause vibrations at all inputs. Thus, there is not a simple one-to-one relationship between loads and inputs. This coupling then can easily lead to false identification of significant paths in case of the OPA method.
Identifying speaker-dependent acoustic parameters in Spanish vowels
Authors: Marrero Victoria , Battaner Elena , Gil Juana , Llisterri Joaquim , Machuca María , Marquina Montserrat , De La Mota Carme , Rios Antonio
Published: May 2008

In the frame of VILE Projects (Inter-and-Intra-Speaker-Variation-in-Spanish for automatic speaker identification), we try to identify what vowel's acoustic parameters depend more on the individual characteristics of the speaker and less of the linguistic variables. Variations on standard deviation (SD), when grouping together parameters by speaker or by phoneme, are analysed. 30 speakers (from AHUMADA database) read the same text in three sessions. Mean value (Hz) of four formants (F1-F2-F3-F4) and fundamental frequency (F0) are analysed in Spanish vowels (except /u/), surrounded by unvoiced stops or /s/ (1850 samples). Hypothesis: Individual parameters will show less SD when grouping by speaker/session; vowel quality parameters, when grouping by phoneme. F1 and F2 are timbre-dependent parameters. F3 and F4 are speaker-dependent parameters. F0 has characteristics of both. The most variable parameter is F2. The opposite is F4. -No significant differences grouping by session or by speakers in none of the parameters. -F0 has the highest variability between vowel qualities, even if stressed and unstressed vowels are separated. -When clustering data by speaker/sessión (all vowels together), by comparison with clustering by vowel (all speakers together), SD is *50% higher in F1-F2 *75% lesser in F4 *66% lesser in F0 *F3 shows no significant differences
Dependence of corresponding phonetic categories in native bilingual speakers and in monolingual overhearers of English and French
Authors: Fowler Carol A.
Published: May 2008

Our research addresses two main questions. First, among phonetic categories that correspond, but are not identical, in the two languages of native bilingual speakers, are there cross-language influences on speech production? Specifically, are the voiceless voice-onset times (VOTs) of bilingual speakers of English and French in Montreal longer in their French speech and shorter in their English speech than the VOTs of monolingual speakers of the two languages in Montreal? Our findings suggest a positive answer. Second, does mere overhearing of a language that one does not speak have an impact on production of phonetic categories? To answer this, we examined the voiceless VOTs of monolingual speakers of French and English in Montreal (who hear substantial unaccented English and French, respectively) with those, respectively, of monolingual speakers of French in Paris and of English in Connecticut. Our answer here was no. I discuss the implications of these findings for an understanding of the phonetic knowledge systems of monolingual and natively bilingual speakers.
Analyze effects of the flow on the vocalic reduction and the coarticulation in sequences CV of pharyngal Arabic
Authors: Falek Leila , Bouferroum Othmane , Djeradi Amar
Published: May 2008

The degree of coarticulation and the vocalic reduction (RV) are indices related to a good engine control (Gay, 1978). Fowler (1998) explains why locus equation (LE) is used to characterize, at the same time, the place of articulation and the degree of coarticulation between consonants and vowels: a strong slope (m=1) indicates a maximum coarticulation between consonants and vowels (i.e., minimal resistance of the coarticulation), while a weak slope (m=0) indicates absence of coarticulation between consonants and vowels (maximum resistance of the coarticulation). The bond between the degree of coarticulation and the RV can be explained according to the linear relation between F2onset and F2milieu: the modifications of values of F2milieu will affect those of F2onset and consequently those of the slopes of. In this study, the analysis of the vocalic reduction and slopes of the equations of locus, carried out on CV (extracts starting from sentences) in standard Arabic pronounced by speakers having different mother tongues (near to Arabic standard and very far away from standard Arabic), and at speed of variable elocution, revealed a vocalic reduction and a variation of the slope of the locus equation, specific to each speaker, who seems to be related to his mother tongue. El Tamimi (2006) carried out a similar study with normal flow, in dialectical Arabic and in French, with normal flow, an influence of the mother tongue showed on the vocalic reduction and the slope of the equation of locus.
A comparison between two cases of voicing neutralization: Final devoicing and voicing assimilation in obstruent clusters
Authors: Campos-Astorkiza Rebeka
Published: May 2008

This study compares two processes that result in voicing neutralization, namely final obstruent devoicing and regressive voicing assimilation in obstruent clusters in Lithuanian. The goal is to find out whether both neutralizing environments present similar acoustic patterns. Acoustic data was collected from native speakers of Lithuanian in order to analyze /k/ and /g/ in word final position (final devoicing) and in the word medial clusters /gs/, /ks/, /kz/ and /gz/ (voicing assimilation). Three main acoustic cues to obstruent voicing were measured: obstruent closure duration, voicing during closure and duration of preceding vowel. The statistical results show that, although both final devoicing and voicing assimilation result in incomplete voicing neutralization, they use the acoustic cues differently. In the case of voicing assimilation, there are statistically significant differences in closure duration, voicing during closure and preceding vowel duration between the stops in /ks, gz/ and their assimilated counterparts in /gs, kz/. As for final devoicing, underlyingly voiceless obstruents and devoiced obstruents show differences in their closure duration and voicing during closure but not in their preceding vowel duration. These results suggest that final devoicing and voicing assimilation have different acoustic realizations in Lithuanian, supporting their analysis as two different processes.
Breathy and whispery voicing in White Hmong
Authors: Fulop Sean , Golston Chris
Published: May 2008

Two phonatory strategies are acknowledged to involve a superposition of periodic vocal cord vibration with excessive airflow generating turbulent noise. Breathy voice has the vocal folds vibrating along their entire length, but incomplete closure allows a constant airflow. Whispery voice has the vocal folds vibrating modally along an anterior segment, while the arytenoids maintain a posterior hole which allows a constant airflow. In linguistic phonetics, these are standardly regarded as variant strategies of a single “breathy voice'' specification, and have never been noted to coexist in one language in an important way. They do in White Hmong. One of the seven “tones'' of White Hmong is breathy. Syllables bearing this tone display breathy voicing (of the first type) on the vowel. White Hmong also has a stop [dh], which sounds like whispery voicing during the release phase. In this study, the breathy tone is shown to have a higher H1 amplitude relative to H2 (compared to modal voice), while the whispery voiced stop is even more extreme in this measure. Whispery voiced stops are also shown to display less harmonicity than the breathy tone, which in turn has less harmonicity than modal voicing in a similar syllable.
The effect of vowel duration on formant frequencies - data from Hakka Chinese
Authors: Lee Wai-Sum , Zee Eric
Published: May 2008

In the target undershoot model, vowel duration is considered as the main determinant of vowel reduction, resulting in undershoot in formant frequencies relative to the “bull's-eye formant pattern” (Lindblom, 1963). The model predicts more schwa-like formant frequencies as vowel duration is shortened. In Hakka Chinese, vowel phonemes /i e a o u/ may be realized as long [i: e: a: o: u:] in the CV: syllables and short [i e a o u] in the CVS syllables (S=a stop consonant). Results of a formant frequency analysis of the long and short vowel sets in Hakka Chinese from ten male and ten female speakers show that (i) in all the short vowels there is a displacement of vowel formant frequencies away from the target frequencies associated with the long vowels; and (ii) relative to the target frequencies, F1F2 do not become more schwa-like for all the short vowels, with [u] being the only vowel that undergoes centralization in the F1F2 plane and with [i e o a] displaying a significant rise in F1, [i e] an insignificant decrease in F2, and [o] an insignificant increase in F2. It appears that the Hakka data do not support the target undershoot model.
An experimental and modeling study of anticipatory coarticulation in VCV sequences
Authors: Ma Liang , Perrier Pascal , Dang Jianwu
Published: May 2008

Anticipatory coarticulation within V1CV2 sequences is studied for EMMA data in French and in Mandarin Chinese. The corpus was designed consistently for both languages. V1 and V2 were /i, a, u/ and C was either /t/ or /k/. The influences of V2 on tongue position of V1 and of C were analyzed for three French and two Chinese speakers. For French speakers vowel V2 influences the whole sequence V1CV2, while its influence is strictly limited to the syllable CV2 for Mandarin speakers. These suggested that speech planning strategies in French and in Chinese are different and that differences could arise from differences in the status of the syllable in the analyzed languages. A speech production model has been then used for testing quantitatively these conclusions. It involves a forward model and optimization techniques to infer optimal motor commands from the phonemic targets in the perceptual space. Different hypotheses about planning and execution of movement were tested on this model. The comparison of simulations and data supports the hypothesis that the syllable could be a basic unit for planning for Mandarin speakers, while it suggests that larger sequences such as VCV should be considered in the planning of French sequences.
Psychoacoustic measures of blind audio source separation performance
Authors: Lee Mingu , Heo Inseok , Choi Nakjin , Sung Koeng-Mo
Published: May 2008

In this paper, an improved method for evaluating the performance of blind audio source separation (BASS) is discussed. In previous studies, such as described in E. Vincent et al., IEEE Transactions on Speech and Audio Processing, 2006, several computation methods for measuring quality of BASS algorithms e.g., defined by source-to-distortion ratio (SDR), source-to-interferences ratio (SIR), sources-to-noise ratio (SNR) and sources-to-artifacts ratio (SAR) are introduced. However, those methods do not take human auditory system into consideration. An improved method is developed by applying preprocessing and using weighted-inner product in frequency domain instead of simple inner-product in time domain. The proposed method incorporates well-known psychoacoustic characteristics e.g., masking effect and equal loudness contours. In comparison with the conventional quality measures, the proposed method shows better correlation with the results of carefully designed listening tests.
The development of measurable speech rhythm during second language acquisition
Authors: Gutiérrez Díez Francisco , Dellwo Volker , Gavaldà Núria , Rosen Stuart
Published: May 2008

It has been demonstrated repeatedly that durational characteristics of consonantal (C) and vocalic (V) intervals are robust acoustic correlates of rhythm class (stress-timed, syllable-timed, mora-timed). Here, we investigate how objective rhythm measures develop during the acquisition of a second language. In a longitudinal study, nine native speakers of Spanish were recorded reading a text in English before and after a year of English language training at university level. A control group of nine native English speakers read the same text. Automatic forced alignment of speech segment boundaries using hidden Markov models allowed the calculation of C and V interval durations. Standard rhythm metrics (%V, deltaC, deltaV, PVI) were calculated for all recordings. First results show that durational C interval characteristics between native English and Spanish English (pre- and post-training) do not differ. However, V interval characteristics (deltaV, nPVI, %V) are lowest for English natives, higher for the Spanish post training group and highest for the Spanish pretraining group. The results suggest that (a) deficits of speech rhythm competence in a second language are mostly revealed on a vocalic level and (b) an increase in competence in a second language is reflected well by measurable speech rhythm.
Contextual influences: Perception of sentences in noise is facilitated similarly in young and older listeners by meaningful semantic context; neural correlates explored via functional magnetic resonance imaging (fMRI)
Authors: Macdonald Heather , Davis Matthew H. , Pichora-Fuller Kathy , Johnsrude Ingrid S.
Published: May 2008

Meaningful semantic context has been demonstrated to improve comprehension of spoken sentences by young and old adults, especially in difficult listening conditions. Evidence for this benefit is based largely on data collected using SPIN sentences, highly structured sentences with a predictable or unpredictable final word. We asked young (14 participants, aged 18-25) and older adults (20 participants, aged 60-75) to report entire sentences which were less structured in nature and contained either a meaningful or anomalous global semantic context. Sentences were mixed with signal-correlated noise, at 9 signal-to-noise ratios (-6 to +2 dB), and also presented without noise. Comprehension by both groups benefited from meaningful context, without a clear overall difference in the amount of benefit obtained. We used fMRI to look at neural activity associated with deriving benefit from meaningful context. Whole-brain EPI data were acquired from young (16 participants, aged 19-26) adults using a sparse imaging design. Word-report data obtained in the scanner were used as intelligibility measures in data analysis. In addition to activity associated with meaningful context, we observe a large left inferior-frontal region in which BOLD signal correlated more strongly with the intelligibility of anomalous compared to coherent prose, presumably reflecting challenged semantic integration processes.
Vowel duration as a cue for coda voicing and the perception of second-language vowel quantity
Authors: Podlipsky Vaclav Jonas
Published: May 2008

When acquiring the phonology of a second language (L2), a learner may have to dissociate a perceptual cue from what it marked in the first language (L1) and attach it to another linguistic entity. This study examined the acquisition of Czech vowel quantity by native speakers of American English. In Czech, vowel duration is reserved for cuing short/long vowel (V/V:) contrasts, while in English it is an important cue for coda obstruent voicing. It is not certain whether in Czech, as in many other languages, voiced codas lengthen the preceding vowels; if they do, a vowel should be more likely to be perceived as short before a voiced obstruent and as long before a voiceless one. A perceptual V/V: categorization experiment showed that for Czech listeners (n=54) the V/V: boundary came slightly (3.3 ms) but consistently (p<0.001) later before a voiced coda. If English learners transfer L1 perceptual strategies to their L2 Czech, the V/V: boundary shift should be even larger. However, this study found no significant effect of coda voicing on the perception of vowel quantity for the non-native listeners. It is concluded that the learners redefined the value of vowel duration as a perceptual cue.
Expanding the set of acoustic features of the post-vocalic voicing contrast in English
Authors: Rodgers Blake , Purnell Thomas , Salmons Joseph
Published: May 2008

The literature on post-vocalic voicing contrasts indicates that no single acoustic characteristic or perceptual cue captures the phonological distinction [e.g., Nittrouer 2004]. Previous perceptual studies examined such acoustic characteristics as vowel duration, percent and duration of closure voicing, formant, and F0 transitions. Detailed acoustic examination reveals additional variation. It is hypothesized that these understudied acoustic characteristics also play a role in the family of voicing cues. In the present study, two laryngeal characteristics are measured and modeled: glottalization (here, an abrupt drop in rate of vocal fold vibration by tensed vocal folds) and a sharp amplitude drop (due to abrupt spreading of vocal folds). Examination of American English data reveals that speakers tend to have at least one of these two characteristics in their final voiceless obstruents, but generally not both. Results suggest a process of laryngeal enhancement of final voiceless obstruents in addition to the traditional cues of vowel duration, formant transitions, etc. Implications for the categorization of laryngeal features and trading relations within the family of final voicing cues are discussed.
Acoustic characteristics of Swedish dorsal fricatives
Authors: Shosted Ryan
Published: May 2008

The identity of [“hooktop heng”], the “voiceless dorso-palatal/velar fricative” or “simultaneous” [“esh”] and [x], is controversial (IPA 2009: 140, 203). The present study attempts to acoustically differentiate [“esh”], [x], and (non-labialized) [“hooktop heng”]. A female speaker of Stockholm Swedish produced VCV nonsense words with balanced V and alternating C. Windowed spectra were obtained and averaged at various locations in the fricatives. [“esh”] can be reliably differentiated from [x] and [“hooktop heng”] based on center of gravity measures in the middle of the fricative. However, center of gravity differences between [x] and [“hooktop heng”] are not revealing, confirming Lindblad's x-ray tracings (1980: 89). The most robust acoustic difference between the two dorsal fricatives is the presence of erratic, high-amplitude disturbances during [x]. These may be attributed to sudden explosions of saliva and ephemeral contact with the uvula, more likely for slightly-retracted [x] than for [“hooktop heng”]. It seems unlikely that [“hooktop heng”] is produced with a second simultaneous constriction that is of acoustic relevance. International Phonetic Association. 1999. Handbook of the International Phonetic Association. Cambridge: Cambridge University Press. Lindblad, P. 1980. Svenskans sje- och tje-ljud i ett Allmänfonetisk perspektiv. Travaux de l'Institut de linguistique de Lund 16. Lund: LiberLäromedel/Gleerup.
Audiovisual speech perception in children with autism spectrum disorders and typical development
Authors: Irwin Julia
Published: May 2008

For typically developing perceivers, visual speech information influences what listeners hear. When the place of articulation of visual and auditory speech tokens are incongruent, perceivers often report hearing a visually influenced response (the “McGurk effect”, McGurk and MacDonald, 1976). Children with autism spectrum disorders (ASD) appear to be less susceptible to the McGurk effect than their typically developing peers (e.g., Mongillo, Irwin, Whalen, Klaiman, Carter and Schultz, in press). Given the gaze aversion characteristic of children with ASD, eye-tracking methodology was employed to extend our previous research on the McGurk effect to examine: (1) sensitivity to mismatched auditory and visual speech (McGurk), (2) visual gain in the presence of auditory noise, and (3) detection of auditory and visual asynchrony. Children with ASD and their chronological age-matched and verbal mental age-matched typically developing controls (ranging in age from 7-12 years) were assessed. Implications for the development of audiovisual speech processing in typically developing and children with ASD will be discussed. [Work supported by NIH.]
Factors influencing French schwa deletion and duration: A corpus-based study
Authors: Bürki Audrey , Ernestus Mirjam , Fougeron Cécile , Gendrot Cédric , Frauenfelder Ulrich H.
Published: May 2008

Numerous factors have been advanced to account for the alternance of schwa with zero in French, such as lexical frequency, sonority, syllable structure, phonotactic constraints, etc. ... In the present study we use a recently developed statistical modeling technique, mixed effects models with crossed random effects, to capture the relative contributions of multiple linguistic factors on both, schwa deletion and schwa's physical duration when present. This study is based on the analysis of 4300 occurrences, extracted from the production of more than 300 speakers in a broadcast corpus. The implications of these findings for the debate on the nature of the processes involved in schwa deletion as well as for the nature of lexical representations will be discussed.
Perceptual clarity of speech modulates activity in left temporal-lobe regions: fMRI correlates of top-down influences
Authors: Wild Conor , Davis Matthew H. , Hervais-Adelman Alexis G. , Johnsrude Ingrid S.
Published: May 2008

Behavioral evidence supports the idea that perception is guided by mechanisms that compute an input's most probable interpretation. For example, four-band noise-vocoded speech, which is largely unintelligible to naive listeners, becomes perceptually clear when listeners possess prior knowledge of the signal content - a phenomenon we call “pop-out”. Feedback connections within and among auditory cortical regions may allow cognitively “higher” levels of processing to predict and thus “explain” the bottom-up signal. In the present study, we use fMRI to investigate the network underlying pop-out. We use written primes (matching or nonmatching text strings) to manipulate a subject's perception of single noise-vocoded words, thereby creating acoustically matched conditions that elicit the perceptions of intelligible or unintelligible speech. Whole brain fMRI data were gathered from 21 subjects using a sparse-imaging procedure. Preliminary analysis reveals regions of statistically significant signal change along the left superior and middle temporal gyri and superior temporal sulcus for matching trials that induce perceptual popout. Functional connectivity analysis will allow us to investigate coupling among these auditory regions, and how connectivity is modulated depending on the perceptual coherence of a noise-vocoded utterance.
On nasal onset time (NOT) duration of French nasal vowels in function of the preceding consonant types
Authors: Montagu Julie
Published: May 2008

Aerodynamic requirement, a high intra-oral air pressure (Pio), for the production of stop and fricative consonants delays the nasalization (velum opening) of the subsequent nasal vowel. We call this time delay between the onset of the nasal vowel and that of its nasalization as nasal onset time (NOT). The NOT was expected to be longer after voiceless consonants (higher Pio) than after voiced counterparts. The measurement of NOT on simultaneous recordings of speech and nasal signals for 24 Parisian speakers have unexpectedly shown that a greater NOT after voiced stops (38 ms in average corresponding to 17% of total nasal vowel duration) and voiced fricatives (7%) than after voiceless ones, respectively, 14.5% for stops and 4.1% for fricatives. This order is observed regardless of changes in speech rate: NOT is 11.1% with the voiced and 9.3% with the voiceless stops in slow, 17% and 14.5% in normal, and 22.4% and 18.6% in rapid rate. These results suggest that not only the Pio, but also some other factors are involved in the determination of NOT. We shall discuss possible such factors in perception and in production.
Channel estimation for underwater acoustic communications: sparse channels, soft input data, and Bayesian techniques
Authors: Preisig James , Blair Ballard , Li Weichang
Published: May 2008

The problem of estimating the time-varying impulse response of the communications channel is central to creating reliable and high-rate communications links. Past work has shown that by jointly accounting for channel dynamics and sparse channel characteristics, the accuracy of the channel impulse response estimate is improved with a corresponding improvement in communications systems performance. Following a survey of the basic techniques that have been developed, these basic techniques are extended in two ways. The first allows for a more complete accounting for the channel characteristics via apriori distributions on the probabilities of the complex channel tap values and optimized basis functions for sparse channel structure. The second allows for the use of soft input data in the channel estimation process thus making the techniques feasible for iterative channel estimation and data estimation algorithms. The extensions are developed and their performance compared using data from recent shallow water acoustic communications experiments.
Basin-scale time reversal communications
Authors: Song Heechun , Kuperman William A. , Hodgkiss William
Published: May 2008

During November 1994, broadband acoustic signals were transmitted from a 75-Hz source to a 20-element, 700-m vertical array at approximately 3250 km range in the eastern North Pacific Ocean as part of the Acoustic Engineering Test (AET) of the Acoustic Thermometry of Ocean Climate (ATOC) program [Worcester et al., J. Acoust. Soc. Am. 105, 3185-3201 (1999)]. The AET tomography signal can be treated as a binary-phase shift-keying (BPSK) communication signal with an information rate of 37.5 bits/s. With the multipath arrivals spanning 5-8 s, this data represents an extreme case of intersymbol interference (ISI). The AET array data are processed using time reversal combined with frequent channel updates to accommodate channel variations over the 20-min long reception, followed by a single channel decision-feedback equalizer (DFE). The almost error-free performance using all 20 array elements demonstrates the feasibility of time reversal communications. Further, comparable performance of single receive element communications integrating over multiple transmissions indicates that the ocean provided temporal diversity as well as the spatial diversity provided by the array.
Coherent time reversal communications in a shallow multipath environment
Authors: Jastrzebski Slawomir
Published: May 2008

Underwater acoustic channel is one of the less reliable communication channels due to its reverberant properties produced by the surface and the bottom of the sea and Doppler spreading caused by the transmitter and the receiver movements. Strong intersymbol interference (ISI) caused by time-varying multipath environments and relatively fast channel variations are two of the major challenges for practical implementation of coherent underwater acoustic communications. In this paper a phase conjugation is considered as a method for mitigating intersymbol interference in coherent communication and this technique reducing the complexity of underwater receivers. Phase conjugation uses time reversal to remove intersymbol interferences. This method performs the time reversal operation in the computer at the receiver instead of time reversed propagation through the sea. This paper presents numerical simulations results of coherent communications using this technique. Phase conjugation processing in acoustic communications was demonstrated with the transmission of BPSK and QPSK modulation schemes. Different messages were sent simultaneously to different depths at different ranges in 100 m deep shallow water. Simulation results suggest that the phase conjugation technique may be used as a potential application to undersea communications, especially in an environment with significant multipath.
Robust time-division channel-access approach for an ad hoc underwater network
Authors: Foo Kae Yeet , Atkins Philip , Pointer Steve A. , Tiltman Carl P.
Published: May 2008

An ad hoc underwater network is formed by a cluster of stationary nodes that can act as a source, destination, or a relay, in which data packets usually travel across multiple hops. Using a time-division scheme where the propagation delay between the nodes is used as a packet queuing buffer optimizes throughput. This requires accurate knowledge of the relative ranges of all the nodes, a high level of accuracy in time-synchronization, and restricts changes in the position of the nodes especially in the absence of a central server or master node within the network. A method that offers greater robustness is by using a time-slotted approach, where each node is offered a time-slot sufficient for one transmission to reach its maximum effective range. A passive acknowledgment scheme is implemented where a node listens for acknowledgment when the transmitted packet is being relayed. Nodes monitor other time-slots for the opportunity to contend for idle slots in order to enhance throughput. Results obtained from simulations demonstrate that this method is robust in supporting changes in the relative distances between the nodes, and can typically operate with a time synchronization error of up to 1 s.
Development of an ocean surveillance system
Authors: Ananthakrishnan V. , Prabha C , Hariharan Supriya M. , Pillai Saseendran
Published: May 2008

Now-a-days, underwater sensor networks are gaining considerable importance, for Ocean Surveillance applications. A minimally configurable three-node sensor network is found to be capable of performing localization as well as tracking of underwater targets. Each node comprises of a surface buoy having processing modules, controller hardware and support electronics for estimating the direction of arrival. The development of the node system comprising of controller and processing modules is presented in this paper. The controller hardware, consisting of a gear assembly, magnetic compass and a precision digital signal controller, helps in sampling the ocean by way of steering the hydrophone arrays and capturing the target emanations, while the processing module performs the computation of the direction of arrivals. The target emissions picked up by the hydrophone arrays are analyzed and processed for computing the direction of signal arrival with reference to the geomagnetic meridian. The direction of maximum signal arrivals computed by the three nodes, lead to the estimation of the target position. Localization of the target is carried out by effectively utilizing the information furnished by Global Positioning System incorporated in the node hardware, which has an efficient power management mechanism, as well.
A comparison between modeled and measured high frequency bottom backscattering
Authors: Simons Dick G. , Snellen M.
Published: May 2008

Compared to taking many sediment grabs, classification techniques based on acoustic remote sensing allow for significant cost reductions, providing the required information at much denser spatial scale. An attractive approach hereto is to use the multibeam-echosounder (MBES) which measures sediment backscatter strengths as a function of angle. By maximizing the match between this backscatter strength and model results, sediment properties can be derived. The backscatter model used here accounts for both surface roughness and volume scattering. MBES measurements (300 kHz) were taken in the Cleaver-Bank area (North Sea), characterized by a wide variety of sediment types for which a large number of grabs is collected. For the majority of the sediment types occurring, well-defined single-sediment-type areas can be discerned. Based on MBES measurements in these areas and corresponding geotechnical sediment parameters provided by grab grain size analysis, calibration curves are derived, representing the mismatch between modeled and measured backscatter strengths. These curves are found to be similar for all sediment types considered. By applying these correction curves to the MBES measurements, they show good agreement with the model for all observed sediment types. It is shown that after this correction the model can be used for sediment classification purposes.
High frequency scattering from discrete inclusions in marine sediments
Authors: Ivakin Anatoliy N.
Published: May 2008

A model of high frequency scattering from sediments with discrete inclusions (such as shells and shell fragments) having an arbitrary size-depth distribution is developed. The model assumes also knowledge of a depth-dependent individual scattering function of inclusions. It is more general than in previous models and includes discrete scatterers located both below and on the water-sediment interface (partially buried). Some simple results are obtained for the case of high enough frequencies using approaches of geometry acoustics. Frequency-angular dependencies of the bottom backscattering strength are calculated for sediments with different size-depth distributions of inclusions. Inputs for the size distribution of inclusions (shell fragments) are obtained from granulometric analysis of coarse fractions of the sediment samples taken at the SAX99/SAX04 site (near Ft Walton Beach, Florida). It is shown that taking into account partially buried shells is important and can significantly enhance estimates of the bottom scattering strength especially at grazing angles below critical (about 30 degrees for sand). [Work supported by ONR, Ocean Acoustics].
Clustered scatterers: the effect on the mean acoustic field
Authors: Weber Thomas C.
Published: May 2008

Clustering, or spatially dependent correlation in the fluctuating number density of discrete scatterers of sound, is commonly found to occur in nature. In the ocean, clustering can occur as a result of scatterer entrainment in fluid flows, as in the case of particles and bubbles, or, in the case of fish, as a result of the behaviour of the scatterer. In either case, the presence of clustering can dramatically alter the effect of the scatterers on acoustic fields from that which would be predicted from the same scatterer population but without clustering. The effect of scatterers on the mean acoustic field is often treated using an effective medium wave number. In this paper, a modification to the effective medium number that accounts for clustering is presented and examined for the case of propagation through bubble clouds. Attenuation predictions over a broad range of frequencies (10-350 kHz) using observations of bubble clustering under oceanic breaking waves will be discussed.
Broadband acoustic scattering from nonlinear internal solitary waves
Authors: Lavery Andone
Published: May 2008

High-frequency broadband (150-600 kHz) acoustic scattering techniques have been used to obtain high-resolution images of nonlinear internal solitary waves (ISWs) propagating shoreward over the New Jersey continental shelf. In contrast to traditional single-frequency measurements, broadband acoustic scattering allows the frequency spectrum of the scattering to be determined, which, in combination with scattering models and direct ground-truthing measurements, allows regions in which the scattering is dominated by biology versus microstructure to be distinguished. Multiple ISWs were tracked and imaged acoustically at different stages of their generation, propagation, and dissipation. Simultaneous microstructure and zooplankton net sampling measurements were performed. Multiple scattering layers and distinct scattering patches were often associated to the ISWs, often exhibiting distinct frequency responses. Clear day/night differences in the scattering from the ISWs were observed due to the daily vertical migration of zooplankton. Though high turbulence levels are associated with ISWs, the strongest scattering returns were not always associated to the highest turbulence levels. Instead, the strongest scattering, at some frequencies, was sometimes associated to large temperature gradients. In regions in which the scattering was dominated by either microstructure or zooplankton, acoustic inversions have been performed for the dissipation rate of turbulent kinetic energy and zooplankton size and abundance.
Ten key papers in synthetic aperture sonar
Authors: Gough Peter T. , Hayes Michael
Published: May 2008

There are now hundreds of patents and papers on synthetic aperture sonar; some of them of key importance whereas many others are of peripheral or minor interest. Here we take what we consider to be the top ten publications in synthetic aperture sonar and explain why we believe they are important and how they have made a significant contribution to the developing discipline or have made some leap of imagination in the area. This paper is more than a catalogue of the top ten citations since not all the real advances in the field have been published in academic peer-review journals.