Subglottal Resonances Research Articles

A quantal model for Algerian vowel features identification using formants and subglottal resonances

A quantal model for Algerian vowel features identification using formants and subglottal resonances

Subglottal resonances in healthy older adults

Resonances of the subglottal airways impact the vocal tract transfer function and voice production during speech through linear and non-linear acoustic coupling. It has been posited that subglottal resonances form acoustic boundaries between contrasting sets of vowels and consonants based on their coupling effects on formant frequencies. Thus far, studies of subglottal resonances have reported data almost exclusively from children and young adults; data from older adults are rare. This study investigates subglottal resonances in eight healthy older adults between 50 and 80 years of age (5 males, 3 females). Initial analyses indicate that the first and especially the second subglottal resonances are at lower frequencies than expected when compared against height-matched young adults but that the subglottal resonance frequencies are not dependent on posture, vowel acoustics, or standard measures of pulmonary function.

Acoustics of Breath Noises in Human Speech: Descriptive and Three-Dimensional Modeling Approaches.

Breathing is ubiquitous in speech production, crucial for structuring speech, and a potential diagnostic indicator for respiratory diseases. However, the acoustic characteristics of speech breathing remain underresearched. This work aims to characterize the spectral properties of human inhalation noises in a large speaker sample and explore their potential similarities with speech sounds. Speech sounds are mostly realized with egressive airflow. To account for this, we investigated the effect of airflow direction (inhalation vs. exhalation) on acoustic properties of certain vocal tract (VT) configurations. To characterize human inhalation, we describe spectra of breath noises produced by human speakers from two data sets comprising 34 female and 100 male participants. To investigate the effect of airflow direction, three-dimensional-printed VT models of a male and a female speaker with static VT configurations of four vowels and four fricatives were used. An airstream was directed through these VT configurations in both directions, and their spectral consequences were analyzed. For human inhalations, we found spectra with a decreasing slope and several weak peaks below 3 kHz. These peaks show moderate (female) to strong (male) overlap with resonances found for participants inhaling with a VT configuration of a central vowel. Results for the VT models suggest that airflow direction is crucial for spectral properties of sibilants, /ç/, and /i:/, but not the other sounds we investigated. Inhalation noise is most similar to /ə/ where airflow direction does not play a role. Inhalation is realized on ingressive airflow, and inhalation noises have specific resonance properties that are most similar to /ə/ but occur without phonation. Airflow direction does not play a role in this specific VT configuration, but subglottal resonances may do. For future work, we suggest investigating the articulation of speech breathing and link it to current work on pause postures. https://doi.org/10.23641/asha.24520585.

Development of vowel acoustics and subglottal resonances in American English-speaking children: A longitudinal Study

Acoustic analysis of typically developing elementary school-aged (prepubertal) children’s speech has been primarily performed on cross-sectional data in the past. Few studies have examined longitudinal data in this age group. For this presentation, we analyze the developmental changes in the acoustic properties of children’s speech using data collected longitudinally over four years (from first grade to fourth grade). Four male and four female children participated in this study. Data were collected once every year for each child. Using these data, we measured the four-year development of subglottal acoustics (first two subglottal resonances) and vowel acoustics (first four formants and fundamental frequency). Subglottal acoustic measurements are relatively independent of context, and average values were obtained for each child in each year. Vowel acoustics measurements were made for seven vowels (i, ɪ, ɛ, æ, ʌ, ɑ, u), each occurring in two different words in the stressed syllable. We investigated the correlations between the children’s subglottal acoustics, vowel acoustics, and growth-related variables such as standing height, sitting height, and chronological age. Gender-, vowel-, and child-specific analyses were carried out in order to shed light on how typically developing speech acoustics depend on such variables. [Work supported, in part, by the NSF.]

Classification of voice quality using neck-surface acceleration: Comparison with glottal flow and radiated sound

The aim of the present study is to investigate the usefulness of features extracted from miniature accelerometers attached to speaker's tracheal wall below the glottis for classification of phonation type. The performance of the accelerometer features is evaluated relative to features obtained from inverse filtered and radiated sound. While the former is a good proxy for the voice source, obtaining robust voice source features from the latter is considered difficult since it also contains information about the vocal tract filter. By contrast, the accelerometer signal is largely unaffected by the vocal tract and although it is shaped by subglottal resonances and the transfer properties of the neck tissue, these properties remain constant within a speaker. For this reason, we expect it to provide a better approximation of the voice source than the raw audio. We also investigate which aspects of the voice source are derivable from the accelerometer and microphone signals. Five trained singers (two females and three males) were recorded producing the syllable [pæ:] in three voice qualities (neutral, breathy and pressed) and at three pitch levels as determined by the participants' personal preference. Features extracted from the three signals were used for classification of phonation type using a random forest classifier. In addition, accelerometer and microphone features with highest correlation with the voice source features were identified. The three signals showed comparable classification error rates, with considerable differences across speakers both with respect to the overall performance and the importance of individual features. The speaker-specific differences notwithstanding, variation of phonation type had consistent effects on the voice source, accelerometer and audio signals. With regard to the voice source, AQ, NAQ, L1L2 and CQ all showed a monotonic variation along the breathy - neutral - pressed continuum. Several features were also found to vary systematically in the accelerometer and audio signals: HRF, L1L2 and CPPS (both the accelerometer and the audio), as well as the sound level (for the audio). The random forest analysis revealed that all of these features were also among the most important for the classification of voice quality. Both the accelerometer and the audio signals were found to discriminate between phonation types with an accuracy approaching that of the voice source. Thus, the accelerometer signal, which is largely uncontaminated by vocal tract resonances, offered no advantage over the signal collected with a normal microphone.

Vocal Tract and Subglottal Impedance in High Performance Singing: A Case Study

The respiratory process is important in vocal training and in professional singing, the airflow is highly important. It is hypothesized that subglottal resonances are important to the singing voice in high performance singing. Single subject, prospective. A professional soprano singer shaped her vocal tract to form the vowels [a], [e], [i], [o], and [u] at the pitch d4. We measured phonated vowels and the vocal tract impedance spectra with a deterministic noise supplied by an iPhone buzzer in the range of 200 to 4,000 Hz at closed glottis, during exhalation and during inhalation while maintaining the shape of the vocal tract. Measurements of the phonated vowels before and after the different glottal adjustments were highly reproducible. Vocal tract resonances and the ones resulting during respiration are reported. The impedance spectra show vowel dependent resonances with closed and open glottis. The formants of the vocal spectra are explained by including both, the vocal tract, and the subglottal resonances. The findings indicate that subglottal resonances influence the first formant as well as the singers's formant cluster in high-performance singing. The instrumental setup used for the impedance measurement allows a simple and lightweight procedure for a measurement of vocal tract and subglottal resonances.

Automated vowel space measurement of young children

Vowel formant frequencies are frequently reported as a measure of the articulatory workspace and have been used to study speech development and speech disorders across the lifespan. It is widely acknowledged that the measurement of F1/F2 frequencies for Vowel Space Area (VSA) estimation is a cumbersome task, wrought with challenges and uncertainties. Although there have been advancements in automated approaches, many of these tools continue to be challenged by child speech due to the anatomical differences and dynamic changes of the supraglottal, glottal, and subglottal regions of the airway during the years of speech development. This study examines automated VSA estimation in 4-year-old children using models that have been adapted to manage the higher fundamental frequencies, wider formant bandwidths, and higher amplitudes of subglottal resonances detected in child speech. The speech of six, native American English-speaking, four-year-old children with no history of hearing or speech disorders were included in this investigation. 48 words, including eight American English vowels, were analyzed using traditional manual methods and the SpeechMark MATLAB toolbox automated VSA estimator. The toolbox automates the generation of a convex hull enclosing the child VSA and computation of the area while accounting for the anatomical/acoustic differences that occur during early speech development.

Subglottal pressure oscillations in anechoic and resonant conditions and their influence on excised larynx phonations

Excised larynges serve as natural models for studying behavior of the voice source. Acoustic resonances inside the air-supplying tubes below the larynx (i.e., subglottal space), however, interact with the vibratory behavior of the larynges and obscure their inherent vibration properties. Here, we explore a newly designed anechoic subglottal space which allows removing its acoustic resonances. We performed excised larynx experiments using both anechoic and resonant subglottal spaces in order to analyze and compare, for the very first time, the corresponding subglottal pressures, electroglottographic and radiated acoustic waveforms. In contrast to the resonant conditions, the anechoic subglottal pressure waveforms showed negligible oscillations during the vocal fold contact phase, as expected. When inverted, these waveforms closely matched the inverse filtered radiated sound waveforms. Subglottal resonances modified also the radiated sound pressures (Level 1 interactions). Furthermore, they changed the fundamental frequency (fo) of the vocal fold oscillations and offset phonation threshold pressures (Level 2 interactions), even for subglottal resonance frequencies 4–10 times higher than fo. The obtained data offer the basis for better understanding the inherent vibratory properties of the vocal folds, for studying the impact of structure-acoustic interactions on voice, and for validation of computational models of voice production.

Vocal tract shape and acoustic adjustments of children during phonation into narrow flow-resistant tubes.

The goal of the study is to quantify the salient vocal tract acoustic, subglottal acoustic, and vocal tract physiological characteristics during phonation into a narrow flow-resistant tube with 2.53 mm inner diameter and 124 mm length in typically developing vocally healthy children using simultaneous microphone, accelerometer, and 3D/4D ultrasound recordings. Acoustic measurements included fundamental frequency (fo), first formant frequency (F1), second formant frequency (F2), first subglottal resonance (FSg1), and peak-to-peak amplitude ratio (Pvt:Psg). Physiological measurements included posterior tongue height (D1), tongue dorsum height (D2), tongue tip height (D3), tongue length (D4), oral cavity width (D5), hyoid elevation (D6), pharynx width (D7). All measurements were made on eight boys and ten girls (6-9 years) during sustained /o:/ production at typical pitch and loudness, with and without flow-resistant tube. Phonation with the flow-resistant tube resulted in a significant decrease in F1, F2, and Pvt:Psg and a significant increase in D2, D3, and FSg1. A statistically significant gender effect was observed for D1, with D1 higher in boys. These findings agree well with reported findings from adults, suggesting common acoustic and articulatory mechanisms for narrow flow-resistant tube phonation. Theoretical implications of the findings are discussed.

Subglottal resonances of American English speaking children.

This paper presents an investigation of children's subglottal resonances (SGRs), the natural frequencies of the tracheo-bronchial acoustic system. A total of 43 children (31 male, 12 female) aged between 6 and 18 yr were recorded. Both microphone signals of various consonant-vowel-consonant words and subglottal accelerometer signals of the sustained vowel /ɑ/ were recorded for each of the children, along with age and standing height. The first three SGRs of each child were measured from the sustained vowel subglottal accelerometer signals. A model relating SGRs to standing height was developed based on the quarter-wavelength resonator model, previously developed for adult SGRs and heights. Based on difficulties in predicting the higher SGR values for the younger children, the model of the third SGR was refined to account for frequency-dependent acoustic lengths of the tracheo-bronchial system. This updated model more accurately estimates both adult and child SGRs based on their heights. These results indicate the importance of considering frequency-dependent acoustic lengths of the subglottal system.

Robust speaker identification via fusion of subglottal resonances and cepstral features

This paper investigates the use of subglottal resonances (SGRs) for noise-robust speaker identification (SID). It is motivated by the speaker specificity and stationarity of subglottal acoustics, and the development of noise-robust SGR estimation algorithms which are reliable at low SNRs for large datasets. A two-stage framework is proposed which combines the SGRs with different cepstral features. The cepstral features are used in the first stage to reduce the number of target speakers for a test utterance, and then SGRs are used as complementary second-stage features to conduct identification. Experiments with the TIMIT and NIST 2008 databases show that SGRs, when used in conjunction with PNCCs and LPCCs, can improve the performance significantly (2-6% absolute accuracy improvement) across all noise conditions in mismatched situations.

Robust speaker identification via fusion of subglottal resonances and cepstral features.

This letter investigates the use of subglottal resonances (SGRs) for noise-robust speaker identification (SID). It is motivated by the speaker specificity and stationarity of subglottal acoustics, and the development of noise-robust SGR estimation algorithms which are reliable at low signal-to-noise ratios for large datasets. A two-stage framework is proposed which combines the SGRs with different cepstral features. The cepstral features are used in the first stage to reduce the number of target speakers for a test utterance, and then SGRs are used as complementary second-stage features to conduct identification. Experiments with the TIMIT and NIST 2008 databases show that SGRs, when used in conjunction with power-normalized cepstral coefficients and linear prediction cepstral coefficients, can improve the performance significantly (2%-6% absolute accuracy improvement) across all noise conditions in mismatched situations.

The role of vocal tract and subglottal resonances in producing vocal instabilities

During speech and singing, the vibrating vocal folds are acoustically loaded by resonant ducts upstream (the trachea) and downstream (the vocal tract). Some models suggest that the vocal fold vibration (at frequency fo) is more stable at frequencies below that of a vocal tract resonance, so that the downstream load is inertive (mass-like). If so, vocal fold vibration might become unstable when fo and resonance frequencies "cross over" and the load varies rapidly in phase and magnitude. In one experiment, singers produced a slow diphthong at constant pitch, thus shifting the first tract resonance R1 across fixed fo. In another, pitch glides took fo across the tract and subglottal resonances. Few instabilities occurred when singers could change lip geometry and thus alter R1. This suggests that avoiding resonance crossings can aid vibrational stability. In experiments in which R1 was constrained using a mouth ring, instabilities occurred at frequencies above R1. When subjects sang into an acoustically infinite pipe, which provided a purely resistive load at the lips, R1 was eliminated. Here, instabilities were reduced and concentrated near the lower limit of the head voice.

The role of subglottal resonances in speech processing algorithms

Inspired by Ken Stevens’ work on speech production, we investigated the role of the subglottal resonances (SGRs) in several machine-based speech processing algorithms. The subglottal acoustic system refers to the acoustic system below the glottis, which consists of the trachea, bronchi, and lungs. The work is based on the observations that the first and second subglottal resonances (Sg1 and Sg2) form phonological vowel feature boundaries, and that SGRs, especially Sg2, are fairly constant for a given speaker across phonetic contexts and languages. After collecting an acoustic and subglottal database of 50 adults and 48 children, analyzing the database, and developing algorithms to robustly estimate SGRs, we were able to use these resonances to improve the performance of a variety of speech processing algorithms including: recognition of children's speech in limited-data situations, frequency-warping for adult speech recognition, speaker recognition and speaker verification, and automatic height estimation. [Work supported in part by the NSF.]

Relationship between lung volumes and subglottal resonances

Subglottal resonances are dependent the anatomical structure of the lungs, but efforts to detect changes in subglottal resonances throughout an utterance have failed to show any effect of lung volume. In this study, we present the results of an experiment investigating the relationship between lung volumes and subglottal resonances. The pulmonary subdivisions for several speakers were established using a whole-body plethysmograph. Subsequently, lung volume and subglottal resonances were recorded simultaneously using a spirometer and an accelerometer while the speakers produced long sustained vowels.

The role of subglottal acoustics in speech production and perception

In this talk, we present an overview of subglottal acoustics, with emphasis on the significant anatomical structures that define subglottal resonances, and we present results from our experiments incorporating subglottal resonances into automatic speaker normalization and speech recognition technologies. Speech samples used in the modeling and perception studies were obtained from a new speech corpus (the UCLA-WashU subglottal database) of simultaneous microphone and (subglottal) accelerometer recordings of 50 adult speakers of American English (AE). We will discuss new findings about the Young's Modulus of tracheal soft tissue, the viscosity of tracheal cartilage, and the effect of going from a circular cross-section to a rectangular cross-section in the conus elasticus. We also present results from studies demonstrating a small, but significant, role of subglottal resonances in discriminating speaker height and of the interaction between subglottal resonances and formants in height discrimination.

Do subglottal resonances lead to quantal effects resulting in the features [back] and [low]?: A review

A question of general interest is why languages have the sound categories that they do. K. N. Stevens proposed the Quantal Theory of phonological contrasts, suggesting that regions of discontinuity in the articulatory-acoustic mapping serve as category boundaries. H. M. Hanson and K. N. Stevens [Proc. ICPhS, 182–185, 1995] modeled the interaction of subglottal resonances with the vocal-tract filter, showing that when a changing supraglottal formant strays into the territory of a stationary tracheal formant, a discontinuity in supraglottal formant frequency and attenuation of the formant peak occurs. They suggested that vowel space and quality could thus be affected. K. N. Stevens [Acoustic Phonetics, MIT Press, 1998] went further, musing that because the first and second subglottal resonances lead to instabilities in supraglottal formant frequency and amplitude, vowel systems would benefit by avoiding vowels with formants at these frequencies. Avoiding the first subglottal resonance would naturally lead to the division of vowels into those with a low vs. non-low tongue body; avoiding the second would lead to the division of vowels into those having a back vs. front tongue body. We will review subsequent research that offers substantial support for this hypothesis, justifying inclusion of the effects of subglottal resonances in phonological models.

Impact of subglottal resonances on bifurcations and register changes in laboratory models of phonation

Many laboratory studies of phonation have failed to fully specify the subglottal system employed during research. Many of these same studies have reported a variety of nonlinear phenomena, such as bifurcations and vocal register changes. While such phenomena are often presumed to result from changes in the biomechanical properties of the larynx, such phenomena may also be a manifestation of coupling between the voice source and the subglottal tract. Using laboratory models of phonation, a variety of examples will be given of nonlinear phenomena induced by both laryngeal and subglottal mechanisms. Moreover, using tracheal tube lengths commonly reported in the literature, it will be shown that most of the nonlinear phenomena commonly reported in voice production may be replicated solely on the acoustical resonances of the subglottal system. Finally, recommendations will be given regarding the experimental design of laboratory experiments which may allow laryngeally induced bifurcations to be distinguished from subglottally induced bifurcations.

Estimating Speaker Height and Subglottal Resonances Using MFCCs and GMMs

This letter investigates the use of MFCCs and GMMs for 1) improving the state of the art in speaker height estimation, and 2) rapid estimation of subglottal resonances (SGRs) without relying on formant and pitch tracking (unlike our previous algorithm in [1]). The proposed system comprises a set of height-dependent GMMs modeling static and dynamic MFCC features, where each GMM is associated with a height value. Furthermore, since SGRs and height are correlated, each GMM is also associated with a set of SGR values (known a priori). Given a speech sample, speaker height and SGRs are estimated as weighted combinations of the values corresponding to the N most-likely GMMs. We assess the importance of using dynamic MFCC features and the weighted decision rule, and demonstrate the efficacy of our approach via experiments on height estimation (using TIMIT) and SGR estimation (using the Tracheal Resonance database.

Acoustic features mediating height estimation from human speech

The current experiment was aimed at providing the first direct evidence regarding the role of subglottal resonances in height discrimination. Past research has investigated whether or not listeners are able to discriminate which of two talkers is taller (Rendall et al., 2007), but has not established what parameters of the acoustic speech signal listeners use to distinguish speaker height. In the current study, we examined the role of subglottal resonances in height discrimination. Subglottal resonances generally refer to resonances of the lower airways starting in the lungs and terminating at the glottis. Subglottal resonances would be a good candidate for use in height estimation because they remain relatively stable across vowels and are relatively unaffected by other factors influencing the supra-laryngeal vocal tract; instead they are influenced nearly exclusively by the lower airway acoustic properties. Listeners participated in two tasks, the first task was a two-alternative forced choice (2AFC) height discrimination test, in which listeners heard sentences produced by two talkers of the same gender and were asked to determine which of the two was the tallest. The second task involved listening to five talkers (all same gender) sentences, and then ranking those individuals from tallest to shortest. Findings indicate that listeners are able to discriminate and rank speakers heights better than chance, and the role of subglottal resonances will be reported.