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Towards vocal-behaviour and vocal-health assessment using distributions of acoustic parameters
Full text linkVoice disorders at different levels are affecting those professional categories that make use of voice in a sustained way and for prolonged periods of time, the so-called occupational voice users. In-field voice monitoring is needed to investigate voice behaviour and vocal health status during everyday activities and to highlight work-related risk factors. The overall aim of this thesis is to contribute to the identification of tools, procedures and requirements related to the voice acoustic analysis as objective measure to prevent voice disorders, but also to assess them and furnish proof of outcomes during voice therapy.
The first part of this thesis includes studies on vocal-load related parameters. Experiments were performed both in-field and in laboratory. A one-school year longitudinal study of teachers’ voice use during working hours was performed in high school classrooms using a voice analyzer equipped with a contact sensor; further measurements took place in the semi-anechoic and reverberant rooms of the National Institute of Metrological Research (I.N.Ri.M.) in Torino (Italy) for investigating the effects of very low and excessive reverberation in speech intensity, using both microphones in air and contact sensors. Within this framework, the contributions of the sound pressure level (SPL) uncertainty estimation using different devices were also assessed with proper experiments.
Teachers adjusted their voice significantly with noise and reverberation, both at the beginning and at the end of the school year. Moreover, teachers who worked in the worst acoustic conditions showed higher SPLs and a worse vocal health status at the end of the school year. The minimum value of speech SPL was found for teachers in classrooms with a reverberation time of about 0.8 s.
Participants involved into the in-laboratory experiments significantly increased their speech intensity of about 2.0 dB in the semi-anechoic room compared with the reverberant room, when describing a map. Such results are related to the speech monitorings performed with the vocal analyzer, whose uncertainty estimation for SPL differences resulted of about 1 dB.
The second part of this thesis was addressed to vocal health and voice quality assessment using different speech materials and devices. Experiments were performed in clinics, in collaboration with the Department of Surgical Sciences of Università di Torino (Italy) and the Department of Clinical Science, Intervention and Technology of Karolinska Institutet in Stockholm (Sweden). Individual distributions of Cepstral Peak Prominence Smoothed (CPPS) from voluntary patients and control subjects were investigated in sustained vowels, reading, free speech and excerpted vowels from continuous speech, which were acquired with microphones in air and contact sensors. The main influence quantities of the estimated cepstral parameters were also identified, which are the fundamental frequency of the vocalization and the broadband noise superimposed to the signal. In addition, the reliability of CPPS estimation with respect to the frequency content of the vocal spectrum was evaluated, which is mainly dependent on the bandwidth of the measuring chain used to acquire the vocal signal.
Regarding the speech materials acquired with the microphone in air, the 5th percentile resulted the best statistic for CPPS distributions that can discriminate healthy and unhealthy voices in sustained vowels, while the 95th percentile was the best in both reading and free speech tasks. The discrimination thresholds were 15 dB (95\% Confidence Interval, CI, of 0.7 dB) and 18 dB (95\% CI of 0.6 dB), respectively, where lower values indicate a high probability to have unhealthy voice. Preliminary outcomes on excerpted vowels from continuous speech stated that a CPPS mean value lower than 14 dB designates pathological voices. CPPS distributions were also effective as proof of outcomes after interventions, e.g. voice therapy and phonosurgery. Concerning the speech materials acquired with the electret contact sensor, a reasonable discrimination power was only obtained in the case of sustained vowel, where the standard deviation of CPPS distribution higher than 1.1 dB (95\% CI of 0.2 dB) indicates a high probability to have unhealthy voice. Further results indicated that a reliable estimation of CPPS parameters is obtained provided that the frequency content of the spectrum is not lower than 5 kHz: such outcome provides a guideline on the bandwidth of the measuring chain used to acquire the vocal signal
Confronto tra sensori a contatto per il monitoraggio vocale
No full textI moderni dispositivi per il monitoraggio vocale prediligono l'utilizzo di microfoni a contatto per diversi motivi: una bassa sensibilità al rumore di fondo acustico, la poca invasività del sensore e più in generale una maggiore facilità di utilizzo rispetto ad un microfono in aria. Il segnale rilevato con uno di tali sensori fissato alla base del collo è legato alla vibrazione della pelle indotta dalle corde vocali. L'obiettivo della ricerca è quello di ricavare informazioni sulla dinamica in ampiezza, sulla risposta in frequenza e sulla sensibilità al rumore di fondo di tali sensori, per individuare quelli più adatti a fornire informazioni equivalenti a quelle ottenute dal segnale vocale rilevato in aria. A tal fine è stata definita un'opportuna procedura di prova a cui è stato sottoposto un campione di diversi soggetti utilizzando 4 diversi sensori: due microfoni ECM di diverse dimensioni, un sensore piezoelettrico e un accelerometr
Variabilità intra e inter-soggetto della misura del livello di pressione sonora
No full textIl presente studio stima le variabilità del livello di pressione sonora (SPL) in un soggetto e in un gruppo di soggetti, dette rispettivamente variabilità intra- e inter-soggetto. 17 studenti hanno letto 2 brani e il segnale è stato acquisito da un fonometro, un microfono ad archetto e un analizzatore vocale. La variabilità è stata valutata per SPL medio, moda e equivalente in ogni dispositivo. La variabilità intra-soggetto massima ottenuta è di 2,0 dB, mentre quella inter-soggetto è di 5,3 dB
Nuovi parametri acustici utili nella diagnostica e nella prevenzione di patologie vocale
No full textL'analisi acustica del segnale vocale è comunemente usata per la valutazione clinica della voce, in quanto le misurazioni acustiche sono facilmente eseguibili e non intrusive. Recentemente le valutazioni ambulatoriali di parametri acustici basati su misure di breve durata sono integrate da monitoraggi sul lungo periodo effettuati tramite dispositivi portatili che utilizzano microfoni a contatto applicati alla base del collo. Le misurazioni acustiche sono in grado di fornire parametri che costituiscono un valido riferimento per la prevenzione e la diagnosi delle patologie vocali. L'analisi acustica della voce si concentra attualmente su parametri ricavati nel dominio del tempo, ma diversi studi hanno evidenziato la loro limitata riproducibilità a favore di parametri spettrali e cepstrali (ad es. il Cepstral Peak Prominence). Il presente lavoro si pone l'obiettivo di determinare la significatività dei diversi parametri nella valutazione delle patologie vocali e di stimare la correlazione tra i giudizi percettivi e le misure acustich
Degradation rate of eight photovoltaic plants: results during six years of continuous monitoring
Full text linkThe results of six years of continuous monitoring are presented in this paper that refer to eight outdoors PhotoVoltaic (PV) plants. The monitored plants are based on different technologies: mono-crystalline silicon (m-Si), poli-crystalline silicon (p-Si), string ribbon silicon, Copper Indium Gallium Selenide (CIGS) thin film and Cadmium Telluride (CdTe) thin film. Mono-crystalline silicon modules and thin-film modules are used both in fixed installation and on x-y tracking systems. The results are expressed in terms of degradation rate of the efficiency of each PV plant, which is estimated from the measurements provided by a multi-channel data-acquisition system that senses both electrical and environmental quantities. A comparison with the electrical characterization of each plant obtained by means of the transient charge of a capacitive load is also proposed. The capacitive-load technique has been implemented immediately after the installation of the PV plants and after 78 months of operation. The obtained results show that both the m-Si plants in fixed installation and on the tracking system had a negligible degradation, while p-Si and string-ribbon Si exhibited a moderate degradation. Higher was the degradation obtained for the thin-film based plants, with a worst behaviour of the plants installed on the tracking systems
Experimental assessment of degradation rate in photovoltaic modules
No full textA test procedure is described in this paper that is conceived to investigate the degradation mechanism of PV modules based on different technologies. Environmental and mechanical stress factors are applied to the modules under investigation and electrical and electroluminescence characterization procedures are implemented to assess the module performance. Preliminary results are reported that refer to the application of the proposed test procedures to two sets of p-Si modules
Uncertainty issues in the experimental assessment of degradation rate of power ratings in photovoltaic modules
Full text linkA test procedure is described in this paper that is conceived to investigate the degradation mechanism of PhotoVoltaic (PV) modules subjected to different stress quantities. The procedure is based on the application of environmental and mechanical stress quantities to the modules under investigation and on the electrical and optical characterization of the same modules. The measurement technique implemented to estimate the maximum power at Standard Test Conditions (STC) of the PV modules is deeply investigated in order to estimate the 95% confidence interval of the estimated parameter. Preliminary results are also reported that refer to the application of the proposed test procedures to two sets of p-Si modules
Effect of vowel context in cepstral and entropy analysis of pathological voices
Full text linkThis study investigates the effect of vowel context (excerpted from speech versus sustained) on two voice quality measures: the cepstral peak prominence smoothed (CPPS) and sample entropy (SampEn). Thirty-one dysphonic subjects with different types of organic dysphonia and thirty-one controls read a phonetically balanced text and phonated sustained [a:] vowels in comfortable pitch and loudness. All the [a:] vowels of the read text were excerpted by automatic speech recognition and phonetic (forced) alignment. CPPS and SampEn were calculated for all excerpted vowels of each subject, forming one distribution of CPPS and SampEn values per subject. The sustained vowels were analyzed using a 41 ms window, forming another distribution of CPPS and SampEn values per subject. Two speech-language pathologists performed a perceptual evaluation of the dysphonic subjects’ voice quality from the recorded text. The power of discriminating the dysphonic group from the controls for SampEn and CPPS was assessed for the excerpted and sustained vowels with the Receiver-Operator Characteristic (ROC) analysis. The best discrimination in terms of Area Under Curve (AUC) for CPPS occurred using the mean of the excerpted vowel distributions (AUC=0.85) and for SampEn using the 95th percentile of the sustained vowel distributions (AUC=0.84). CPPS and SampEn were found to be negatively correlated, and the largest correlation was found between the corresponding 95th percentiles of their distributions (Pearson, r=−0.83, p < 10−3). A strong correlation was also found between the 95th percentile of SampEn distributions and the perceptual quality of breathiness (Pearson, r=0.83, p < 10−3). The results suggest that depending on the acoustic voice quality measure, sustained vowels can be more effective than excerpted vowels for detecting dysphonia. Additionally, when using CPPS or SampEn there is an advantage of using the measures’ distributions rather than their average values.QC 20180129</p
S&N-S Light: an innovative educational tool that controls chatting noise levels in classrooms by encouraging pupils to change their behaviour
No full textPupils talking and moving in a classroom constitute a main source of disturbance during classes, leading to a degraded teaching and learning process. To improve intelligibility under noisy conditions, teachers tend to raise their voice level with possible negative consequences on their vocal health. On the pupils’ side, the exposure to high noise levels decreases their speech processing and understanding abilities, which are directly related to an increase in the perceived annoyance, thus on a general loss of well-being. In this framework, chatting noise may be controlled by directly encouraging pupils to modify their behaviour. Therefore, a patented sound level meter device, namely the S&N-S Light (Speech & Noise Stop-Light), has been used as an educational tool aimed at controlling chatting noise in everyday living environments. S&N-S Light is a light-system based on the variation of a coloured visual feedback according to the increase in the overall sound level. Such device was adopted throughout planned monitorings with two main aims: first, to evaluate its effectiveness as an educational tool in classrooms with pupils (5÷10 years old); second, to investigate whether a game-based challenge is a useful method to reward the motivation and attention of pupils in controlling their voice as a response to the S&N-S Light visual feedback. In-field monitoring was performed in a primary school in Torino (Italy), where five classrooms from first to fifth grade were involved. Preliminary results confirm a decrease of talking noise levels when the visual feedback of S&N-S Light is active compared to its inactive condition. The subjective impression of the teachers provides encouraging outcomes in terms of effectiveness of S&N-S Light as an educational tool. Pupils reported to be interested in monitoring the changes of the coloured visual feedback and increased their responsibility in affecting the learning environment by controlling their voice
Performance comparison of different contact microphones used for voice monitoring
No full textThe aim of this paper consists in comparing the performances of different sensors used as contact microphones for voice monitoring. Four devices are analyzed: two electret condenser microphones which differ in size, an accelerometer and a piezoelectric transducer. The investigation is based on the analysis of the signal acquired at the output of each sensor when it is attached at the jugular notch, to sense the skin vibration induced by the vocal folds activity. This signal is often used to extract vocal parameters, such as sound pressure level, fundamental frequency, time dose, jitter and shimmer, which are of interest for diagnostic purposes as well as for vocal load assessment. Experimental tests were performed in a sound absorbing chamber using different speech materials. During these tests, a calibrated microphone placed at the fixed distance of 17 cm from the speaker's mouth was used to ensure measurement traceability. The signals simultaneously acquired at the output of each contact sensor and of the microphone in front of the speaker's mouth were compared to identify which device better provides exhaustive information of the speech signal. Since the use of these transducers is not intrusive and does not interfere with normal daily activities (e.g. for voice long-term monitoring in working environments), their sensitivity to body movements and to background noise has also been estimated. The frequency response of each sensor compared to one of the signal acquired by the microphone in air was furtherly analyzed
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