Erkki Vilkman

Occupational Safety and Health Aspects of Voice and Speech Professions

A well-functioning voice is an essential tool for one third of the labour force. Vocal demands vary to a great extent between the different voice and speech professions. In professions with heavy vocal loading (e.g. school and kindergarten teachers), occupational voice disorders threatening working ability are common. Vocal loading is a combination of prolonged voice use and additional loading factors (e.g. background noise, acoustics, air quality) affecting the fundamental frequency, type and loudness of phonation or the vibratory characteristics of the vocal folds as well as the external frame of the larynx. The prevention and treatment of occupational voice disorders calls for improved occupational safety and health (OSH) arrangements for voice and speech professionals. On the basis of epidemiological and acoustic-physiological research, the presence of risk to vocal health can be substantiated. From the point of view of the physical load on the vocal apparatus, loading-related physiological changes (adaptation) may play a role in the occupational risk. Environmental factors affect vocal loading changes. In teaching professions, the working environment is shared with children, who benefit from amendments of OSH legislation concerning their teachers.

Voice Problems at Work: A Challenge for Occupational Safety and Health Arrangement

In modern societies about one third of the labor force are working in professions in which voice is the primary tool. Voice problems are common in general, but they are even more common in professions in which there is heavy vocal loading, i.e. professions that do not only require prolonged voice use, but also involve extra loading factors such as background noise, long speaking distance, poor room acoustics, lack of adequate equipment like voice amplifiers etc. School and kindergarten teachers can be considered to represent professions with heavy vocal loading. The occupational safety and health arrangements of voice and speech professionals are poorly developed as compared to many other professions. However, the existing legislation could be used to support efforts to improve the working conditions of this large but heterogeneous group.

Normalized amplitude quotient for parametrization of the glottal flow

Normalized amplitude quotient (NAQ) is presented as a method to parametrize the glottal closing phase using two amplitude-domain measurements from waveforms estimated by inverse filtering. In this technique, the ratio between the amplitude of the ac flow and the negative peak amplitude of the flow derivative is first computed using the concept of equivalent rectangular pulse, a hypothetical signal located at the instant of the main excitation of the vocal tract. This ratio is then normalized with respect to the length of the fundamental period. Comparison between NAQ and its counterpart among the conventional time-domain parameters, the closing quotient, shows that the proposed parameter is more robust against distortion such as measurement noise that make the extraction of conventional time-based parameters of the glottal flow problematic. Experiments with breathy, normal, and pressed vowels indicate that NAQ is also able to separate the type of phonation effectively.

Voice Changes During Work: Subjective Complaints and Objective Measurements for Female Primary and Secondary Schoolteachers

The purpose of this investigation was to study voice changes during a working day. The subjects consisted of 33 female primary and secondary schoolteachers who recorded their first and last lessons during one school day. The subjects were studied both as one group and two subgroups (those with many and those with few voice complaints). Estimates of fundamental frequency (F0), sound pressure level (SPL), the standard deviations of these values (F0 SD; SPL SD) and F0 time (vibration time of vocal folds) were made. The most obvious change due to loading was the rise of F0 that was 9.7 Hz between the first and last lesson (P = 0.00). F0 increased more (12.8. Hz, P = 0.006) in the subgroup with few complaints.

External laryngeal frame function in voice production revisited: A review

Research indicates significant contribution of extrinsic laryngeal mechanisms to voice production. This article reviews the major theories of the role of the external laryngeal factors in voice production and relevant experimental data. The review suggests that partly neglected external factors and possibly even misinterpretation of some of the recently documented individual variation in physiological data may have unnecessarily complicated the issues pertaining to the interplay between the physiological mechanisms of the larynx. The implications of contemporary findings and documentation in the modeling of the extrinsic factors are discussed and a synthesis of empirical data into two simple models of the extrinsic forces of pitch control is presented. Also suggested by the review, a basic principle, probably underlying the laryngeal control of phonation, is put forward.

A comparison of Glottal Voice Source Quantification Parameters in Breathy, Normal and pressed Phonation of Female and Male Speakers

This study concerns a comparison of different quantification techniques that have been developed to parameterize a voice source that has been estimated using inverse filtering that applies no flow mask (i.e. absolute flow values are not obtained). The speech material consisted of voices of three different phonation types produced by 5 female and 5 male subjects. Quantification of the voice source was computed using three time-based quotients that were extracted from the glottal flow waveforms, two time-based parameters that were extracted from the flow and its first derivative, one amplitude-domain quotient that was defined using both the flow and its derivative, and one frequency domain parameter that was computed from the flow signal. The results showed that phonation types could be separated from each other most effectively when quantification was based on parameters that were extracted between the instant of the maximal glottal opening and the minimum peak of the flow derivative.

Effects of voice training and voice hygiene education on acoustic and perceptual speech parameters and self-reported vocal well-being in female teachers

Voice education programs may help in optimizing teachers’ voice use. This study compared effects of voice training (VT) and voice hygiene lecture (VHL) in 60 randomly assigned female teachers. All 60 attended the lecture, and 30 completed a short training course in addition. Text reading was recorded in working environments and analyzed for fundamental frequency (F0), equivalent sound level (Leq), alpha ratio, jitter, shimmer, and perceptual quality. Self-reports of vocal well-being were registered. In the VHL group, increased F0 and difficulty of phonation and in the VT group decreased perturbation, increased alpha ratio, easier phonation, and improved perceptual and self-reported voice quality were found. Both groups equally self-reported increase of voice care knowledge. Results seem to indicate improved vocal well-being after training.

Objective Analysis of Vocal Warm-Up with Special Reference to Ergonomic Factors

Vocal warm-up was studied in terms of changes in voice parameters during a 45-minute vocal loading session in the morning. The voices of a randomly chosen group of 40 female and 40 male young students were loaded by having them read a novel aloud. The exposure groups (5 females and 5 males per cell) consisted of eight combinations of the following factors: (1) low (25 +/- 5%) or high (65 +/- 5%) relative humidity of ambient air; (2) low [< 65 dB(SPL)] or high [> 65 dB(SPL)] speech output level during vocal loading; (3) sitting or standing posture during vocal loading. Two sets of voice samples were recorded: a resting sample before the loading session and a loading sample after the loading session. The material recorded consisted of /pa:ppa/ words produced normally, as softly and as loudly as possible in this order by all subjects. The long /a/ vowel of the test word was inverse-filtered to obtain the glottal flow waveform. Time domain parameters of the glottal flow [open quotient (OQ), closing quotient (CQ), speed quotient (SQ), fundamental frequency (F0)], amplitude domain parameters of the glottal flow [glottal flow (fAC) and its logarithm, minimum of the first derivative of the glottal flow (dpeak) and its logarithm, amplitude quotient (AQ), and a new parameter, CQAQ], intraoral pressure (p), and sound pressure level (SPL) values of the phonations were analyzed. Voice range profiles (VRP) and the singers formant (g/G, a/A, cl/c, e1/e, g1/g for females/males) of the loud phonation were also measured. Statistically significant differences between the preloading and postloading samples could be seen in many parameters, but the differences depended on gender and the type of phonation. In females the values of CQ, AQ, and CQAQ decreased and the values of SQ and p increased in normal phonations; the values of fAC, dpeak, and SPL increased in soft phonations; the values of AQ and CQAQ decreased in loud phonations; the harmonic energy in the singers formant region increased significantly at every pitch. In males the values of OQ and AQ decreased and the values of dpeak, F0, p, and SPL increased in normal phonations; the values of fAC and p increased in soft phonations. The changes could be interpreted as signs of a shift toward hyperfunctional voice production. Low humidity was associated with more hyperfunctional changes than high humidity. High output was associated with more hyperfunctional changes than low output. Sitting position was associated with an increasing trend at both margins of male VRP, whereas the case was the opposite for standing position.

Amplitude domain quotient for characterization of the glottal volume velocity waveform estimated by inverse filtering

Abstract An amplitude-domain quotient for parametrization of the glottal source computed by inverse filtering is presented. The new quotient, AQ, is determined as the ratio between the amplitude of the AC-flow of the glottal waveform and the amplitude of the minimum of the flow derivative. This quotient can be used even though absolute flow values are not given by the recording equipment. The behaviour of AQ was compared to conventional time-based quotients by analysing voices produced by different phonation types. It was shown that phonation types can be quantified effectively when parametrization of the glottal flow estimated by inverse filtering is based on AQ.

Working-Day Effects on the Spectral Characteristics of Teaching Voice

Ten teachers made recordings during one normal working day using a portable DAT recorder and a head-mounted microphone. In addition, the subjects filled in a questionnaire of signs of vocal fatigue. The speech samples were selected from the first and last lesson from three points representing the beginning, middle and end part of the lesson, respectively. To standardize the samples, 30 [a] vowels from stressed syllables were chosen for spectral analysis. The level of the fundamental and second formant regions (L1), the level of frequency ranges 2–5 kHz (L2) and 5–10 kHz (L5) were measured. From these measurements the parameters L1–L0, L1–L2 and L1–L5 were formed and used in the analyses as well as the energy levels below and above 1 kHz (α). Statistically significant changes were observed in the following parameters: the L1–L2 and L1–L5 differences, and the α ratio. In general, there was an increase in the energy content of the high frequency components due to vocal loading. The subjective reports revealed a statistically significant relationship with the spectral characteristics.