manufacturing-process-for-non-adhesive-super-soft-vocal-fold-models

Manufacturing Process for Non-Adhesive Super-Soft Vocal Fold Models

This study aims to develop super-soft, non-sticky vocal fold models for voice research. The conventional manufacturing process of silicone-based vocal ...

Technische Universität Dresden

The role of the vocal tract for phonation at very high soprano fundamental frequencies (F0s) is not yet understood in detail. In this investigation, two experiments were carried out with a single professional high soprano subject. First, using two dimensional (2D) dynamic real-time magnetic resonance imaging (MRI) (24 fps) midsagittal and coronal vocal tract shapes were analyzed while the subject sang a scale from Bb5 (932 Hz) to G6 (1568 Hz). In a second experiment, volumetric vocal tract MRI data were recorded from sustained phonations (13 s) for the pitches C6 (1047 Hz) and G6 (1568 Hz). Formant frequencies were measured in physical models created by 3D printing, and calculated from area functions obtained from the 3D vocal tract shapes. The data showed that there were only minor modifications of the vocal tract shape. These changes involved a decrease of the piriform sinus as well as small changes of tongue position. Formant frequencies did not exhibit major differences between C6 and G6 for F1 and F3, respectively. Only F2 was slightly raised for G6. For G6, however, F2 is not excited by any voice source partial. Therefore, this investigation was not able to confirm that the analyzed professional soprano subject adjusted formants to voice source partials for the analyzed F0s.

Articulation and vocal tract acoustics at soprano subject's high fundamental frequencies.

Recently, 3D printing has been increasingly used to create physical models of the vocal tract with geometries obtained from magnetic resonance imaging. These printed models allow measuring the vocal tract transfer function, which is not reliably possible in vivo for the vocal tract of living humans. The transfer functions enable the detailed examination of the acoustic effects of specific articulatory strategies in speaking and singing, and the validation of acoustic plane-wave models for realistic vocal tract geometries in articulatory speech synthesis. To measure the acoustic transfer function of 3D-printed models, two techniques have been described: (1) excitation of the models with a broadband sound source at the glottis and measurement of the sound pressure radiated from the lips, and (2) excitation of the models with an external source in front of the lips and measurement of the sound pressure inside the models at the glottal end. The former method is more frequently used and more intuitive due to its similarity to speech production. However, the latter method avoids the intricate problem of constructing a suitable broadband glottal source and is therefore more effective. It has been shown to yield a transfer function similar, but not exactly equal to the volume velocity transfer function between the glottis and the lips, which is usually used to characterize vocal tract acoustics. Here, we revisit this method and show both, theoretically and experimentally, how it can be extended to yield the precise volume velocity transfer function of the vocal tract.

How to precisely measure the volume velocity transfer function of physical vocal tract models by external excitation.

This study analyzed the durational and spectral differences and their interaction in the production of seven German tense-lax vowel pairs between 30 German native speakers and 30 Mandarin learners of German. The results showed that Mandarin speakers differed significantly from the German speakers in producing the German tense-lax contrast. The general pattern was that Mandarin learners employed temporal features more strongly than spectral features to indicate the tense-lax contrast as compared to German speakers. The phonetic influences of the Mandarin language on the production of German tense and lax vowels are discussed.

An acoustic comparison of German tense and lax vowels produced by German native speakers and Mandarin Chinese learners.

A detailed understanding of how the acoustic patterns of speech sounds are generated by the complex 3D shapes of the vocal tract is a major goal in speech research. The Dresden Vocal Tract Dataset (DVTD) presented here contains geometric and (aero)acoustic data of the vocal tract of 22 German speech sounds (16 vowels, 5 fricatives, 1 lateral), each from one male and one female speaker. The data include the 3D Magnetic Resonance Imaging data of the vocal tracts, the corresponding 3D-printable and finite-element models, and their simulated and measured acoustic and aerodynamic properties. The dataset was evaluated in terms of the plausibility and the similarity of the resonance frequencies determined by the acoustic simulations and measurements, and in terms of the human identification rate of the vowels and fricatives synthesized by the artificially excited 3D-printed vocal tract models. According to both the acoustic and perceptual metrics, most models are accurate representations of the intended speech sounds and can be readily used for research and education.

Printable 3D vocal tract shapes from MRI data and their acoustic and aerodynamic properties.

The influence of non-smooth trachea walls on phonation onset and offset pressures and the fundamental frequency of oscillation were experimentally investigated for three different synthetic vocal fold models. Three models of the trachea were compared: a cylindrical tube (smooth walls) and wavy-walled tubes with ripple depths of 1 and 2 mm. Threshold pressures for the onset and offset of phonation were measured at the lower and upper ends of each trachea tube. All measurements were performed both with and without a supraglottal resonator. While the fundamental frequency was not affected by non-smooth trachea walls, the phonation onset and offset pressures measured right below the glottis decreased with an increasing ripple depth of the trachea walls (up to 20% for 2 mm ripples). This effect was independent from the type of glottis model and the presence of a supraglottal resonator. The pressures at the lower end of the trachea and the average volume velocities showed a tendency to decrease with an increasing ripple depth of the trachea walls but to a much smaller extent. These results indicate that the subglottal geometry and the flow conditions in the trachea can substantially affect the oscillation of synthetic vocal folds.

Effect of wavy trachea walls on the oscillation onset pressure of silicone vocal folds.

Early detection of malign patterns in patients' biological signals can save millions of lives. Despite the steady improvement of artificial intelligence-based techniques, the practical clinical application of these methods is mostly constrained to an offline evaluation of the patients' data. Previous studies have identified organic electrochemical devices as ideal candidates for biosignal monitoring. However, their use for pattern recognition in real time was never demonstrated. Here, we produce and characterize brain-inspired networks composed of organic electrochemical transistors and use them for time-series predictions and classification tasks using the reservoir computing approach. To show their potential use for biofluid monitoring and biosignal analysis, we classify four classes of arrhythmic heartbeats with an accuracy of 88%. The results of this study introduce a previously unexplored paradigm for biocompatible computational platforms and may enable development of ultralow-power consumption hardware-based artificial neural networks capable of interacting with body fluids and biological tissues.

Reservoir computing with biocompatible organic electrochemical networks for brain-inspired biosignal classification.

When pitch is explicitly modelled for parametric speech synthesis, microprosodic variations of the fundamental frequency f are usually disregarded by current intonation models. While there are numerous studies dealing with the nature and the origin of microprosody, little research has been done on its audibility and its effect on the naturalness of synthetic speech. In this work, the influence of obstruent-related microprosodic variations on the perceived naturalness of articulatory speech synthesis was studied. A small corpus of 20 German words and sentences was re-synthesized using the state-of-the-art articulatory synthesizer VocalTractLab. The pitch contours of the real utterances were extracted and fitted with the Target-Approximation-Model. After the real microprosodic variations were removed from the obtained pitch contours, synthetic variations were applied based on a microprosody model. Subsequently, multiple stimuli with different microprosody amplitudes were synthesized and evaluated in a listening experiment. The results indicate that microprosodic variations are barely audible, but can lead to a greater perceived naturalness of the synthesized speech in certain cases.

Modelling microprosodic effects can lead to an audible improvement in articulatory synthesis.

Resonance-strategies with respect to vocal registers, i.e., frequency-ranges of uniform, demarcated voice quality, for the highest part of the female voice are still not completely understood. The first and second vocal tract resonances usually determine vowels. If the fundamental frequency exceeds the vowel-shaping resonance frequencies of speech, vocal tract resonances are tuned to voice source partials. It has not yet been clarified if such tuning is applicable for the entire voice-range, particularly for the top pitches. We investigated professional sopranos who regularly sing pitches above C6 (1047 Hz). Dynamic three-dimensional (3D) magnetic resonance imaging was used to calculate resonances for pitches from C5 (523 Hz) to C7 (2093 Hz) with different vowel configurations ([a:], [i:], [u:]), and different contexts (scales or octave jumps). A spectral analysis and an acoustic analysis of 3D-printed vocal tract models were conducted. The results suggest that there is no exclusive register-defining resonance-strategy. The intersection of fundamental frequency and first vocal tract resonance was not found to necessarily indicate a register shift. The articulators and the vocal tract resonances were either kept without significant adjustments, or the f:f-tuning, wherein the first vocal tract resonance enhances the fundamental frequency, was applied until F6 (1396 Hz). An f:f-tuning was not observed.

Investigation of resonance strategies of high pitch singing sopranos using dynamic three-dimensional magnetic resonance imaging.

The periodic repetitions of laryngeal adduction and abduction gestures were uttered by 16 subjects. The movement of the cuneiform tubercles was tracked over time in the laryngoscopic recordings of these utterances. The adduction velocity and abduction velocity were determined objectively by means of a piecewise linear model fitted to the cuneiform tubercle trajectories. The abduction was found to be significantly faster than the adduction. This was interpreted in terms of the biomechanics and active control by the nervous system. The biomechanical properties could be responsible for a velocity of abduction that is up to 51% higher compared to the velocity of adduction. Additionally, the adduction velocity may be actively limited to prevent an overshoot of the intended adduction degree when the vocal folds are approximated to initiate phonation.

Velocity differences in laryngeal adduction and abduction gestures.

Recovering speech in the absence of the acoustic speech signal itself, i.e., silent speech, holds great potential for restoring or enhancing oral communication in those who lost it. Radar is a relatively unexplored silent speech sensing modality, even though it has the advantage of being fully non-invasive. We therefore built a custom stepped frequency continuous wave radar hardware to measure the changes in the transmission spectra during speech between three antennas, located on both cheeks and the chin with a measurement update rate of 100 Hz. We then recorded a command word corpus of 40 phonetically balanced, two-syllable German words and the German digits zero to nine for two individual speakers and evaluated both the speaker-dependent multi-session and inter-session recognition accuracies on this 50-word corpus using a bidirectional long-short term memory network. We obtained recognition accuracies of 99.17% and 88.87% for the speaker-dependent multi-session and inter-session accuracy, respectively. These results show that the transmission spectra are very well suited to discriminate individual words from one another, even across different sessions, which is one of the key challenges for fully non-invasive silent speech interfaces.

Silent speech command word recognition using stepped frequency continuous wave radar.

This study compared the f of 14 German vowels in monosyllabic words (/dVt/) embedded in carrier sentences produced by 30 native speakers and 30 Mandarin Chinese learners. Appropriate techniques were employed to robustly measure f values and reliably analyze f profiles. The results showed that Mandarin learners produced the vowels bearing sentence stress with significantly larger f ranges and steeper f slopes but comparable f mean and maximum in comparison to German natives. Moreover, lax vowels produced by both groups demonstrated narrower ranges with faster f changes than tense vowels, which was stronger for Mandarin learners.

Comparing fundamental frequency of German vowels produced by German native speakers and Mandarin Chinese learners.

In this study, 23 subjects produced cyclic transitions between rounded vowels and unrounded vowels as in /o-i-o-i-o-…/ at two specific speaking rates. Rounded vowels are typically produced with a lower larynx position than unrounded vowels. This contrast in vertical larynx position was further amplified by producing the unrounded vowels with a higher pitch than the rounded vowels. The vertical larynx movements of each subject were measured by means of object tracking in laryngeal ultrasound videos. The results indicate that larynx lowering was on average 26% faster than larynx raising, and that this velocity difference was more pronounced in woman than in men. Possible reasons for this are discussed with a focus on specific biomechanical properties. The results can help to interpret vertical larynx movements with regard to underlying neural control and aerodynamic conditions, and to improve movement models for articulatory speech synthesis.

Intrinsic velocity differences between larynx raising and larynx lowering.

In this study, silicone vocal fold models with different geometries were manufactured using the common silicone brand EcoFlex 00-30 with typical oil mixing ratios. However, the proportions of oil typically used are higher than the manufacturer's recommended limit, in order to attain the softness of human vocal folds. This additional oil causes direct effects on the silicone, such as shrinkage, stickiness, evaporation, embrittlement, and uneven vulcanization. This study investigated the impact of these effects on the oscillation characteristics of the silicone vocal fold models and how they change over time. The goal was to examine the comparability of produced silicone vocal fold models and the results obtained from experiments performed with these models. For the manufactured models, the phonation onset pressure, offset pressure, mean volume velocity, pulmonary power, fundamental frequency, and measures of the glottal area waveform were collected over a period of up to 8 weeks. The results showed that the data for the models were highly scattered. Furthermore, over time, the phonation onset/offset pressures increased, leading to failure to oscillate for some models, and the glottal area waveform also changed. In conclusion, when working with over-thinned silicone vocal fold models, their characteristics depend strongly on the time of measurement. Therefore, it is recommended to carefully consider the effects of oil-oversaturation and timing of measurements when using silicone vocal fold models in experiments.

Reproducibility and Aging of Different Silicone Vocal Folds Models.

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.

Article	Year
Articulation and vocal tract acoustics at soprano subject's high fundamental frequencies. The Journal of the Acoustical Society of America\| PubMed ID: 25994691	2015
How to precisely measure the volume velocity transfer function of physical vocal tract models by external excitation. PloS one\| PubMed ID: 29543829	2018
An acoustic comparison of German tense and lax vowels produced by German native speakers and Mandarin Chinese learners. The Journal of the Acoustical Society of America\| PubMed ID: 32752753	2020
Printable 3D vocal tract shapes from MRI data and their acoustic and aerodynamic properties. Scientific data\| PubMed ID: 32759947	2020
Effect of wavy trachea walls on the oscillation onset pressure of silicone vocal folds. The Journal of the Acoustical Society of America\| PubMed ID: 33514162	2021
Reservoir computing with biocompatible organic electrochemical networks for brain-inspired biosignal classification. Science advances\| PubMed ID: 34407948	2021
Modelling microprosodic effects can lead to an audible improvement in articulatory synthesis. The Journal of the Acoustical Society of America\| PubMed ID: 34470273	2021
Investigation of resonance strategies of high pitch singing sopranos using dynamic three-dimensional magnetic resonance imaging. The Journal of the Acoustical Society of America\| PubMed ID: 34972262	2021
Velocity differences in laryngeal adduction and abduction gestures. The Journal of the Acoustical Society of America\| PubMed ID: 35105025	2022
Silent speech command word recognition using stepped frequency continuous wave radar. Scientific reports\| PubMed ID: 35273225	2022
Comparing fundamental frequency of German vowels produced by German native speakers and Mandarin Chinese learners. JASA express letters\| PubMed ID: 36154640	2021
Intrinsic velocity differences between larynx raising and larynx lowering. PloS one\| PubMed ID: 36795744	2023
Reproducibility and Aging of Different Silicone Vocal Folds Models. Journal of voice : official journal of the Voice Foundation\| PubMed ID: 36966126	2023
Acoustics of Breath Noises in Human Speech: Descriptive and Three-Dimensional Modeling Approaches. Journal of speech, language, and hearing research : JSLHR\| PubMed ID: 37971432	2023

Peter Birkholz

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