Frequency Contours Research Articles

A first vocal repertoire characterization of long-finned pilot whales (Globicephala melas) in the Mediterranean Sea: a machine learning approach.

The acoustic repertoires of long-finned pilot whales (Globicephala melas) in the Mediterranean Sea are poorly understood. This study aims to create a catalogue of calls, analyse acoustic parameters, and propose a classification tree for future research. An acoustic database was compiled using recordings from the Alboran Sea, Gulf of Lion and Ligurian Sea (Western Mediterranean Basin) between 2008 and 2022, totalling 640 calls. Using a deep neural network, the calls were clustered based on frequency contour similarities, leading to the identification of 40 distinct call types defining the local population's vocal repertoire. These categories encompass pulsed calls with varied complexities, from simplistic to highly intricate structures comprising multiple elements and segments. This study marks the initial documentation of the vocal catalogue of long-finned pilot whales in the Mediterranean Sea. Subsequent research should delve deeper into this multifaceted communication system and explore its potential linkages with social structures.

Processing group delay spectrograms for study of formant and harmonic contours in speech signals.

This paper deals with study of formant and harmonic contours by processing the group delay (GD) spectrograms of speech signals. The GD spectrum is the negative derivative of the phase spectrum with respect to frequency. Recent study shows that the GD spectrogram can be obtained without phase wrapping. Formant frequency contours can be observed in the display of the peaks of the instantaneous wideband equivalent GD spectrogram, derived using the modified single frequency filtering (SFF) analysis of speech signals. Harmonic frequency contours can be observed in the display of the peaks of the instantaneous narrowband equivalent GD spectrogram, derived using the modified SFF analysis of speech signals. For synthetic speech signals, the observed formant contours match the ground truth formant contours from which the signal is derived. For natural speech signals, the observed formant contours match approximately with the given ground truth formant contours mostly in the voiced regions. The results are illustrated for several randomly selected utterances from the TIMIT database. While this study helps to observe the contours of formants in the display, automatic extraction of the formant frequencies needs further processing, requiring logic for eliminating the spurious points, without forcing the number of formants.

Assessment of ISRO’s S-band polarimetric Doppler Weather Radar (DWR) at SHAR with IMD-DWR and GPM-Ku radar

ABSTRACT This paper describes the first assessment of ISRO’s indigenously developed S-band Polarimetric Doppler Weather Radar (DWR) at Sriharikota High Altitude Range (SHAR), Sriharikota (13.66°N, 80.23°E). The assessment is done during the passage of a tropical cyclone ‘Phethai’ and four different cases of Mesoscale convective systems. A comparison of reflectivity measured from SHAR-DWR with India Meteorological Department (IMD) DWR located at Chennai (13.07°N, 80.28°E) and Ku-band space-borne radar of the Global Precipitation Mission (GPM) is done using the common volume matching method. A good comparison is observed between SHAR-DWR with IMD-DWR and GPM-Ku radar in both space and height. The vertical structure of the cyclone is provided using Contour Frequency by Altitude Diagrams (CFAD) which show the vertical extent up to an altitude of 16 km with a reflectivity between 25 and 30 dBZ. Maximum occurrence of 30 dBZ occurs below 6 km. Bright band signatures show ~ 25 dBZ between 4 and 5 km depicting the stratiform precipitation of the cyclone. Further rain rate is estimated using both reflectivity and the polarimetric product which compared well with rain estimated from IMD-DWR and rainfall observed from rain gauges. Rain rate is observed from 5 to 35 mm hr−1. Hydrometer classification during the passage of tropical cyclone ‘Phethai’ shows the presence of rain below 4 km and graupels, ice crystals, and large droplets above.

Nonlinear response of very high frequency contour mode resonators

We explore the source of nonlinearities in Aluminum Nitride (AlN) Contour Mode Resonators (CMRs) operating in the Very High Frequency (VHF) range. We demonstrate that the red-shift of the resonance frequency found in VHF CMRs when the input RF power increases is due to nonlinear stiffness appearing from self-heating, and variable damping due to geometric nonlinearities. Moreover, we find a linear relationship between the variable damping coefficient and the resonator quality factor (Q). Such nonlinear mechanisms are modeled using a spring-mass-damper physical system and, in the electrical domain, a modified Butterworth-Van Dyke (MBVD) circuit where the nonlinear stiffness and variable damping are captured by a charge-dependent motional capacitor and a charge-dependent motional resistor, respectively. Detailed guidelines are provided to accurately analyze nonlinear CMRs using full-wave numerical simulations based on a finite-element method. Such simulations allow us to isolate the influence of each independent nonlinear mechanism and establish a relation between variable damping and geometric nonlinearities. Circuit and full-wave numerical simulations are in good agreement with measured data from fabricated 225 MHz CMRs exhibiting different Q. Finally, we exploit nonlinearities in high-Q CMRs to generate frequency combs at the MHz range opening the door to new exciting applications in telecommunication and sensing.

STRAIGHTMORPH: A Voice Morphing Tool for Research in Voice Communication Sciences

The purpose of this paper is to make easily available to the scientific community an efficient voice morphing tool called STRAIGHTMORPH and provide a short tutorial on its use with examples. STRAIGHTMORPH consists of a set of Matlab functions allowing the generation of high-quality, parametrically-controlled morphs of an arbitrary number of voice samples. A first step consists in extracting an ‘mObject’ for each voice sample, with accurate tracking of the fundamental frequency contour and manual definition of Time and Frequency anchors corresponding across samples to be morphed. The second step consists in parametrically combining the mObjects to generate novel synthetic stimuli, such as gender, identity or emotion continua, or random combinations. Although STRAIGHTMORPH has been designed for human voices it can work well with other types of sounds such as non-human primate vocalizations.

Boundary of the Distribution of Solar Wind Proton Beta versus Temperature Anisotropy

The frequency distribution of solar wind protons, measured in the vicinity of Earth’s orbit, is customarily plotted in (β ∥, T ⊥/T ∥) phase space. Here, T ⊥/T ∥ is the ratio of perpendicular and parallel temperatures, and β ∥ = 8π nT ∥/B 2 is the ratio of parallel thermal energy to background magnetic field energy, the so-called “parallel beta,” with ⊥ and ∥ denoting directions with respect to the ambient magnetic field. Such a frequency distribution, plotted as a two-dimensional histogram, forms a peculiar rhombic shape defined with an outer boundary in the said phase space. Past studies reveal that the threshold conditions for temperature anisotropy–driven plasma instability partially account for the boundary on the high-β ∥ side. The low-β ∥ side remains largely unexplained despite some efforts. Work by Vafin et al. recently showed that certain contours of collisional relaxation frequency, ν pp, when parameterized by T ⊥/T ∥ and β ∥, could match the overall shape of the left-hand boundary, thus suggesting that the collisional relaxation process might be closely related to the formation of the left-hand boundary. The present paper extends the analysis by Vafin et al. and carries out the dynamical computation of the collisional relaxation process for an ensemble of initial proton states with varying degrees of anisotropic temperatures. The final states of the relaxed protons are shown to closely match the observed boundary to the left of the (β ∥, T ⊥/T ∥) phase space. When coupled with a similar set of calculations for the ensemble in the collective instability regime, it is found that the combined collisional/collective effects provide the baseline explanation for the observation.

Intelligently optimized arch-honeycomb metamaterial with superior bandgap and impact mitigation capacity

Engineering applications concurrently face challenges related to vibration, impact, load-bearing and energy absorption. Here, an arch-honeycomb metamaterial with split-ring resonators is proposed for wave attenuation and impact mitigation, with better energy absorption and lower initial peak stress. The split-ring resonators effectively induce bandgaps below 3 kHz, and the mechanisms of bandgap generation and polarization are studied through mode shapes, frequency contours and equivalent mass densities. Subsequently, a machine learning-based optimization framework is introduced to tailor the bandgaps, leading to a 155.59% increase in bandgap width. Furthermore, superior vibration isolation and impact mitigation are confirmed through experiments. Obvious attenuation peaks are observed in the bandgaps of the acceleration transmission spectrum in frequency domain. In time domain, the impact test demonstrates peak weakening and delay. The metamaterials offer advantages in wave attenuation, impact mitigation, load-bearing and energy absorption, providing valuable insights for the advancement of multifunctional metamaterials and their practical engineering applications.

Revisiting the nature and the context of T4 alternations: insights from disyllabic, trisyllabic and quadrisyllabic word/digit productions in Taiwan Mandarin.

The tone values of a Tone 4 (T4) syllable are conventionally assumed to change from '51' to '53' when the syllable is followed by another T4 syllable in Mandarin Chinese. Literature focusing on T4 alternation is still inconclusive regarding the contexts for the alternations and whether the phenomenon should be better categorized as tone sandhi (i.e.,represented as an abstract phonological rule in mental grammar) or tonal coarticulation (i.e.,a natural articulation phenomenon at the phonetic level). The current study probes into these issues by focusing on disyllabic pseudowords, right-branching trisyllabic words as well as unstructured trisyllabic and quadrisyllabic digits. Productions from a total of 148 participants were collected and fundamental frequency (f0) contours, vowel lengths and f0 slopes were included in the analysis. The results from the experiments supported the tonal coarticulation view and showed that the trigger for the alternations was the high-onset tones following T4. Implications to the phonological analysis on tonal alternations in Mandarin Chinese are discussed.

Droplet collection efficiencies inferred from satellite retrievals constrain effective radiative forcing of aerosol–cloud interactions

Abstract. Process-oriented observational constraints for the anthropogenic effective radiative forcing due to aerosol–cloud interactions (ERFaci) are highly desirable because the uncertainty associated with ERFaci poses a significant challenge to climate prediction. The contoured frequency by optical depth diagram (CFODD) analysis supports the evaluation of model representation of cloud liquid-to-rain conversion processes because the slope of a CFODD, generated from joint MODerate Resolution Imaging Spectroradiometer (MODIS)-CloudSat cloud retrievals, provides an estimate of cloud droplet collection efficiency in single-layer warm liquid clouds. Here, we present an updated CFODD analysis as an observational constraint on the ERFaci due to warm rain processes and apply it to the U.S. Department of Energy's Energy Exascale Earth System Model version 2 (E3SMv2). A series of sensitivity experiments shows that E3SMv2 droplet collection efficiencies and ERFaci are highly sensitive to autoconversion, i.e., the rate of mass transfer from cloud liquid to rain, yielding a strong correlation between the CFODD slope and the shortwave component of ERFaci (ERFaciSW; Pearson's R=-0.91). E3SMv2's CFODD slope (0.20 ± 0.04) is in agreement with observations (0.20 ± 0.03). The strong sensitivity of ERFaciSW to the CFODD slope provides a useful constraint on highly uncertain warm rain processes, whereby ERFaciSW, constrained by MODIS-CloudSat, is estimated by calculating the intercept of the linear association between the ERFaciSW and the CFODD slopes, using the MODIS-CloudSat CFODD slope as a reference.

Acquisition of Mandarin tones by Canadian first graders: Effect of prior exposure to tonal and non-tonal languages.

This study examines the tone productions of school-aged children with and without a tonal language background who are learning Mandarin as a second language (L2) or heritage language in Mandarin-English bilingual schools in Western Canada. Tones are frequently identified as one of the most challenging aspects of phonology for Mandarin L2 learners to acquire. In this study, tone productions of bilingual children from three home language backgrounds, English, Cantonese, and Mandarin Chinese, were compared for transcribed accuracy using mixed effects logistic regression. In addition, the fundamental frequency contours of correct tone productions were fitted with generalized additive mixed models to analyse the acoustic differences between groups. Error patterns were also analysed for possible Cantonese substitutions. Our results suggest that children with a Cantonese background are more accurate in tone productions than children with an English language background, but they also made more errors than their peers with a Mandarin language background. These findings suggest that a tonal language background could result in positive transfer among school-age children who are in the early stages of learning Mandarin as an L2.

Lexical Stress Identification in Cochlear Implant-Simulated Speech by Non-Native Listeners.

This study investigates whether a presumed difference in the perceptibility of cues to lexical stress in spectro-temporally degraded simulated cochlear implant (CI) speech affects how listeners weight these cues during a lexical stress identification task, specifically in their non-native language. Previous research suggests that in English, listeners predominantly rely on a reduction in vowel quality as a cue to lexical stress. In Dutch, changes in the fundamental frequency (F0) contour seem to have a greater functional weight than the vowel quality contrast. Generally, non-native listeners use the cue-weighting strategies from their native language in the non-native language. Moreover, few studies have suggested that these cues to lexical stress are differently perceptible in spectro-temporally degraded electric hearing, as CI users appear to make more effective use of changes in vowel quality than of changes in the F0 contour as cues to linguistic phenomena. In this study, native Dutch learners of English identified stressed syllables in CI-simulated and non-CI-simulated Dutch and English words that contained changes in the F0 contour and vowel quality as cues to lexical stress. The results indicate that neither the cue-weighting strategies in the native language nor in the non-native language are influenced by the perceptibility of cues in the spectro-temporally degraded speech signal. These results are in contrast to our expectations based on previous research and support the idea that cue weighting is a flexible and transferable process.

Exploring the frequency contours in close reading texts

Exploring the frequency contours in close reading texts

ANALYSIS OF NATURAL FREQUENCIES FOR EARLY DAMAGE DETECTION IN CFRP SHAFTS USING RSM-BASED FREQUENCY CONTOUR PLOTS

This study explores early damage detection in carbon fiber-reinforced polymer shafts by analyzing natural frequencies. Modern engineering components often face increased flexibility and high stress levels, leading to cracks in rotating parts, which can result in premature failures. To address this issue, modal analysis, specifically natural frequency analysis, is employed to identify deviations caused by cracks. Cracks alter stiffness and mass distribution, leading to shifts in natural frequencies. The study employs finite element models to simulate various crack locations and depths, normalizing them with respect to shaft diameter and length. A cantilever shaft configuration is utilized with refined mesh structures near the transverse crack. The analysis leverages the frequency contour method with response surface methodology to visualize how crack depth and location influence normalized natural frequencies. Results indicate that crack depth has a significant impact on natural frequencies, while crack location has a subtler effect. Combining depth and location produces the most pronounced frequency variations. The corresponding R² values for the normalized first and third natural frequencies are 95.69% and 96.32%, while for the normalized second natural frequency this value is 75.70%. The study also demonstrates the use of frequency contour curves for accurate crack detection, with the 1st and 3rd natural frequencies being reliable indicators.

Dugong chirp type classification based on fundamental contour extraction and hierarchical cluster analysis

A steady decrease in the Dugong (Dugong dugon) population has been notices worldwide. Considering the social function and utilization rate, dugong chirp classification has become an important bioacoustics research topic, which may help marine biologists monitor the change of their population, study their behavioral context in different environments and optimise the protection policy. However, the objective classification of dugong chirps has not been adequately addressed in the literature. In this paper, an automatic fundamental contour extraction using the tempo-frequency variables to describe the contours of the fundamental frequency of the chirps is presented. With the automatic fundamental contour extraction, the time–frequency information of dugong chirps can be effectively represented, which gives a good classification performance. Following the principles used for the classification of dolphin whistles, three variables were chosen and performed with hierarchical cluster analysis. Based on these results and further visual examination, five categories of chirps were identified. A simple classification criterion was proposed which could be used in the automatic and effective identification of chirp types. Our findings enrich the known repertoire of dugong chirps, and may be useful in future passive acoustic monitoring studies.

Band gap tunability and wave propagation of a novel fully symmetric single-phase metamaterial

In this paper, a new type of fully symmetric single-phase metamaterial structure is proposed. Based on the finite element method, the band gap characteristics of different forms of the structure and the generation principle of the band gap are discussed. The analysis of the formation mechanism of the band gap shows that the proposed structure can achieve the purpose of expanding the band gap in the low frequency range by changing the structure and adding inclusions. Then, the variation trend of the band gap frequency range in the case of small deformation of the proposed structure is discussed. In addition, the propagation characteristics of elastic waves in the proposed structure are analyzed according to the variation characteristics of frequency contours, phase velocities and group velocities. Finally, the frequency response spectrum obtained from the propagation of elastic waves in a finite lattice composed of Model No. 3 elements further confirms the role of the proposed structure in suppressing wave propagation. The results show that the proposed structure has good band gap characteristics in a certain frequency range, which can provide ideological guidance for the design of metamaterials for achieve low-frequency sound insulation and vibration reduction.

Passive elimination of flow-induced forces and vibrations of a circular cylinder using a slit

Here, passive flow control technique of incorporating a slit through a circular structure is utilized to dampen the flow-induced vibration (FIV). The study is segregated into two main sections, one where the effect of slit width ratio (S/D) and Reynolds number (Re) is investigated on the fixed stationary cylinder, and the other where the effect of slit size is explored on the behavior of the elastically mounted cylinder with varying reduced velocities (Ur) at Re = 100. The slit width ratio is varied from 0% (no slit) to 50% and Re from 100 to 300 for a stationary cylinder. For elastically mounted cylinder, the mass (m* = 5) and damping (ζ = 0.01) ratios and Re (100) are fixed, whereas Ur is varied from 0 to 10. The results are expressed as coefficient of lift and drag, Strouhal number, amplitude and frequency of vibration, force-displacement plots, and vorticity contours. They indicate that the presence of a slit reduces the lift and drag coefficients and suppresses the FIV. At Re = 100, the presence of 10% and 20% slit decreases the lift coefficient by 13.0% and 71.8%, respectively, as compared to the solid cylinder. Considering the maximum amplitude of vibration, a 10% slit resulted in a 5.7% amplitude drop, whilst a 20% slit resulted in a significant drop of 34.4% as compared to the solid cylinder. Further increasing the slit size from 20% to 30% completely vanished the vortex shedding and led to steady flow with zero lift and no vibration.

On the nature of Tone 4 alternation in Taiwan Mandarin: Insights from acoustic analysis of trisyllabic right-branching word productions

Tone 4 (T4) alternations refer to the phenomenon where the tone values of a T4 syllable reduces from ‘51' to ‘53' when it is followed by another T4 syllable in Mandarin Chinese. It is inconclusive if the nature of T4 alternations is tone sandhi (an abstract phonological rule) (Chao, 1948; Jang, 2021) or tonal coarticulation (an articulatory phenomenon in speech production) (Lin, 20007; Shen, 1990). The current study invited 30 Taiwan Mandarin speakers to produce 10 pairs of right-branching trisyllabic words, including sequences of [T4[T4-T4]] (e.g., dà diàn shì 'big television') and [T4[T4-Tone1]] syllables (e.g., dà diàn jiā ‘big store'). The T4 sandhi view predicted that the surface tone values of the first syllables in these two sequences would differ (“51i” vs. “53”), while the T4 coarticulation view predicted that the tone values would be the same (“53”). Results from the acoustic analysis on fundamental frequency (f0) contour, f0 slope and vowel length of the first T4 syllables indicated that the differences were not statistically significant. These results supported the tonal coarticulation view. Discussions pertaining to the mental grammar for the tone value distances of two adjacent T4 syllables and the typology of tonal coarticulation in Mandarin Chinese are formulated.

Expanding research on ʔayʔaǰuθəm interrogative intonation

Relatively little research has been done on ʔayʔaǰuθəm prosody. This lack of research is due in part to the idea that stress and tone are not distinctive features in the language. However, recent studies have found evidence of suprasegmental features in ʔayʔaǰuθəm interrogatives. Additionally, previous work indicates that—as has been reported with other Salishan languages—there is no significant rise in fundamental frequency at the end of ʔayʔaǰuθəm interrogatives, though the mean vowel fundamental frequency is higher in interrogative than in declarative sentences. These findings are not unique to ʔayʔaǰuθəm, but they do contribute to growing evidence that a final rise in fundamental frequency in interrogative sentences is not universal. In the present study, we aim to address the limitations of our previous work by expanding on the amount of data used, incorporating methods for analyzing the entire fundamental frequency contour, and measuring the mean fundamental frequency of vowels from more balanced stimuli. Although we do not expect different results from the present study, it is our hope that the methodologies used will increase the validity of our findings on ʔayʔaǰuθəm interrogative intonation.

Observation of the geometry-dependent skin effect and dynamical degeneracy splitting

The non-Hermitian skin effect is a distinctive phenomenon in non-Hermitian systems, which manifests as the anomalous localization of bulk states at the boundary. To understand the physical origin of the non-Hermitian skin effect, a bulk band characterization based on the dynamical degeneracy on an equal frequency contour is proposed, which reflects the strong anisotropy of the spectral function. In this paper, we report the experimental observation of a newly-discovered geometry-dependent non-Hermitian skin effect and dynamical degeneracy splitting in a two-dimensional acoustic crystal and reveal their remarkable correspondence by performing single-frequency excitation measurements. Our work not only provides a controllable experimental platform for studying the non-Hermitian physics, but also confirms the unique correspondence between the non-Hermitian skin effect and the dynamical degeneracy splitting, paving a new way to characterize the non-Hermitian skin effect.

Quantifying Shallow-Depth Concrete Delamination using Impact-Echo

Corrosion-induced concrete deck delamination is quite common in bridges. Locating these embedded delaminations is important to assess the extent of the damage, the remaining member capacity and any necessary rehabilitation. The impact-echo (IE) is a simple and straightforward non-destructive testing (NDT) technique by which the depth and extent of concrete delamination may be estimated. It is effective in detecting the location and determining the depth of relatively deep delaminations in concrete. Delaminations that occur near the concrete surface can also be detected by the IE method. However, the exact depth cannot be quantified due to difficulties in analysing the flexural mode that dominates the vibration response over the corresponding delaminated region. This study developed an IE-based procedure to quantitatively estimate the depth of shallow depth delaminations in concrete slab members. Four slab specimens were prepared, each with three artificial delaminations with varying shapes and sizes at shallow depths. The frequency contour maps showed good agreement with the actual location of the delaminations. The perimeter-to-depth ratio of the delaminated region can be used to analyze the flexural mode vibration frequency. Two equations are proposed that relate the depth of arbitrarily shaped delaminations to the flexural mode vibration frequency measured over the shallow-depth delaminations. Keywords: impact echo, concrete delamination, concrete slabs, flexural mode vibration, non-destructive evaluation (NDE)