Reliability of Speaking and Maximum Voice Range Measures in Screening for Dysphonia

Vocal Range Variations Elicited With a Standard Mandarin Reading Passage in Individuals With Voice Disorders

PURPOSE

This study examined whether the "Three Bears Passage" (TB), a standard Mandarin reading passage, could elicit significant vocal range variations in individuals with voice disorders. Relative sensitivity of TB versus another existing standard reading passage, "Passage in Mandarin" (PM), for differentiating between individuals with and without voice disorders was also evaluated.

METHOD

Forty-two individuals with normal voice and 30 individuals with voice disorders participated in the study. Maximum fundamental frequency (f0), minimum f0, mean f0, f0 range, maximum vocal intensity, minimum intensity, mean intensity, and intensity range of all participants reading aloud the two passages were measured with Praat to construct speech range profiles (SRPs).

RESULTS

Significantly larger vocal range was found for TB than for PM in individuals with voice disorders, including significantly higher maximum f0, mean f0, maximum intensity, mean intensity, and significantly larger f0 range and intensity range. Significantly more limited vocal range was observed in individuals with voice disorders than those without, with more obviously restricted SRPs while reading aloud TB compared to PM. Receiver operating characteristic analysis suggested that TB was more sensitive than PM in distinguishing between individuals with and without voice disorders.

CONCLUSIONS

Our findings supported the potential of TB as a standard clinical assessment tool for evaluating pathological changes in vocal range. Future studies should explore if therapeutic approaches based on the passage or variations of it could be developed for overcoming functional limitations and restrictions in vocal range for specific voice disorders.

Normative Voice Range Profile of the Young Female Voice

OBJECTIVES

Normative data are important in the clinical setting of Speech and Language Pathology. The purpose of this study was to develop a normative reference dataset of voice range profiles from young females.

STUDY DESIGN

Descriptive study including a prospective collection of voice range profile data.

METHODS

Voice range profile recordings from 39 females with healthy voices aged 18 to 28 years were conducted. Seven voice range profile variables were analyzed: minimum and maximum fundamental frequency and intensity, semitone and intensity ranges, and voice range profile area. Descriptive statistical methods were applied.

RESULTS

An age-specific voice range profile normative dataset was established. The mean values and standard deviations were as follows: semitone range 34.7 ± 3.9 ST, minimum fundamental frequency 143.6 ± 21.7 hertz, maximum fundamental frequency 1063.5 ± 160 hertz, intensity range 65.6 ± 5.0 dB, minimum intensity 43.2 ± 2.5 dB SPL, maximum SPL 108.9 ± 5.1 dB SPL, and voice range profile area 1346 ± 222 cells.

CONCLUSION

A normative dataset usable for optimization of future voice assessments has been established. It may especially benefit evaluation and treatment planning for younger females suffering from vocal fold nodules.

A mixed-method feasibility study of the use of the Complete Vocal Technique (CVT), a pedagogic method to improve the voice and vocal function in singers and actors, in the treatment of patients with muscle tension dysphonia: a study protocol

BACKGROUND

Muscle tension dysphonia (MTD) results from inefficient or ineffective voice production and is the cause of voice and throat complaints in up to 40% of patients presenting with hoarseness. Standard treatment is voice therapy (SLT-VT) delivered by specialist speech therapists in voice disorders (SLT-V). The Complete Vocal Technique (CVT) is a structured, pedagogic method which helps healthy singers and other performers optimise their vocal function enabling them to produce any sound required. The aim of this feasibility study is to investigate whether CVT administered by a trained, non-clinical CVT practitioner (CVT-P) can be applied to patients with MTD before progressing to a pilot randomised control study of CVT voice therapy (CVT-VT) versus SLT-VT.

METHODS/DESIGN

In this feasibility study, we use a mixed-method, single-arm, prospective cohort design. The primary aim is to demonstrate whether CVT-VT can improve the voice and vocal function in patients with MTD in a pilot study using multidimensional assessment methods. Secondary aims are to assess whether (1) a CVT-VT study is feasible to perform; (2) is acceptable to patients, the CVT-P and SLT-VTs; and (3) whether CVT-VT differs from existing SLT-VT techniques. A minimum of 10 consecutive patients with a clinical diagnosis of primary MTD (types I-III) will be recruited over a 6-month period. Up to 6 video sessions of CVT-VT will be delivered by a CVT-P using a video link. The primary outcome will be a change in pre-/post-therapy scores of a self-reported patient questionnaire (Voice Handicap Index (VHI)). Secondary outcomes include changes in throat symptoms (Vocal Tract Discomfort Scale), acoustic/electroglottographic and auditory-perceptual measures of voice. Acceptability of the CVT-VT will be assessed prospectively, concurrently and retrospectively both quantitatively and qualitatively. Differences from SLT-VT will be assessed by performing a deductive thematic analysis of CVT-P transcripts of therapy sessions.

CONCLUSION

This feasibility study will provide important data to support whether to proceed with a randomised controlled pilot study focusing on the effectiveness of the intervention compared to standard SLT-VT. Progression criteria will be based on demonstrating a positive outcome in treatment, successful delivery of the pilot study protocol, acceptability to all stakeholders and satisfactory recruitment rates.

TRIAL REGISTRATION

ClinicalTrials.gov website ( NCT05365126 Unique Protocol ID: 19ET004). Registered on 06 May 2022.

Associations of Personality, Physical and Mental Health with Voice Range Profiles

OBJECTIVES

There is evidence in the literature that voice characteristics are linked to mental and physical health. The aim of this explorative study was to determine associations between voice parameters measured by a voice range profile (VRP) and personality, mental and physical health.

STUDY DESIGN

Cross-sectional population-based study.

METHODS

As part of the LIFE-Adult-Study, 2639 individuals aged 18-80 years, randomly sampled from the general population, completed both speaking and singing voice tasks and answered questionnaires on depression, anxiety, life satisfaction, personality and quality of life. The voice parameters used were fundamental frequency, sound pressure level, their ranges and maximum phonation time. The associations were examined with the help of correlation and regression analyses.

RESULTS

Wider ranges between the lowest and highest frequency, between the lowest and highest sound pressure level and longer maximum phonation time were significantly correlated with extraversion and quality of life in both sexes, as well as openness and agreeableness in women. Smaller ranges and shorter maximum phonation time were significantly correlated with depression. Neuroticism in men was inversely correlated with the maximum phonation time. In the speaking VRP, the associations for sound pressure level were more pronounced than for the fundamental frequency. The same was true in reverse for the singing VRP. Few associations were found for anxiety, life satisfaction and conscientiousness.

CONCLUSIONS

Weak associations between voice parameters derived from the VRP and mental and physical health, as well as personality were seen in this exploratory study. The results indicate that the VRP measurements in a clinical context are not significantly affected by these parameters and thus are a robust measurement method for voice parameters.

Sex and Age Stratified Voice Data in Japanese Vocally Healthy Individuals: Vocal Capacity

OBJECTIVE

There is no normative voice dataset regarding the vocal capacity of Japanese speakers in the English literature. We collected age- and sex-stratified data on the vocal capacity of vocally healthy Japanese speakers.

METHODS

In total, 111 vocally healthy Japanese speakers (42 men and 69 women) were divided into the young (13 men and 30 women), middle-aged (18 men and 27 women), and elderly (11 men and 12 women) groups. Participants underwent duration-, intensity-, and pitch-related vocal capacity tests using either a conventional method or an aerodynamic method or both. The data obtained were statistically analyzed in terms of age and sex.

RESULTS

Overall, the duration- and pitch-related parameters measured by the conventional method were generally comparable to the previous results in the literature, while duration-, pitch-, and intensity-related parameters measured by the aerodynamic method differed significantly from them. Significant sex differences were noted in all parameters in the duration-, intensity-, and pitch-related vocal capacity tests. Furthermore, significant age-related changes were observed in all parameters, except for the mean flow rate and highest pitch measured by the aerodynamic method.

CONCLUSION

This study is the first to provide a sex- and age-stratified database of the normative vocal capacity data of Japanese speakers. However, further improvements will be needed in the assessment protocols, conditions, or devices used for the duration-, intensity-, and pitch-related vocal capacity tests in the aerodynamic method.

A Mandarin Chinese Reading Passage for Eliciting Significant Vocal Range Variations

Purpose There is a lack of standardized Mandarin reading text material that could potentially elicit significant variations in fundamental frequency (F0) and in vocal intensity for clinical voice evaluation. In this study, a phonetically balanced "Three Bears Passage" was developed based on the classical "Goldilocks" story for this purpose. The hypothesis was that the vocal range (F0 range and Intensity range) elicited while reading aloud the passage could be similar to that of the voice range profile (VRP) obtained with sustained vowel production and significantly different from that while reading an existing standard Mandarin passage. Method One hundred twenty young adults (60 men and 60 women, aged 25.22 ± 3.74 years) without vocal pathologies and vocal training participated in the study. Vocal range data, including F0-related measures and intensity-related measures, were obtained with Praat in order to construct VRPs for the sustained /a/ and to construct speech range profiles for passage reading. Results F0 range and intensity range for the new passage were significantly larger than those for the existing Mandarin passage for both male and female participants. In particular, the F0 range for the passage was not significantly different from that of the VRP for male participants. Conclusions These findings suggested that the new passage could allow individuals without vocal training to demonstrate a large vocal range in both F0 and vocal intensity, in a passage reading setting in a relatively short time. Further studies should be pursued with the passage to investigate the vocal range and vocal potential of individuals with voice disorders.

Data Collection Methods for the Voice Range Profile: A Systematic Review

Purpose To assess data collection variability in the voice range profile (VRP) across clinicians and researchers, a systematic review was conducted to evaluate the extent of variability of specific data collection points that affect the determination of frequency range and sound level and determine next steps in standardization of a VRP protocol. Method A systematic review was conducted using the Preferred Reporting Items for Systematic Review and Meta-Analysis checklist. Full-text journal articles were identified through PubMed, Web of Science, Psych Info, ProQuest Dissertations and Theses Global, Google Scholar, and hand searching of journals. Results A total of 1,134 articles were retrieved from the search; of these, 463 were duplicates. Titles and abstracts of 671 articles were screened, with 202 selected for full-text review. Fifty-four articles were considered eligible for inclusion. The information extracted from these articles revealed the methodology used to derive the VRP was extremely variable across the data points selected. Additionally, there were eight common acoustic measures used for statistical analysis described in included studies that were added as a data point. Conclusions The data collection methods for the VRP varied considerably. Standardization of procedures was recommended for clinicians and researchers.

Standardization and Feasibility of Voice Range Profile Measurements in Epidemiological Studies

OBJECTIVES

The voice range profile (VRP) is composed of the speaking VRP (spVRP) and the singing VRP (siVRP). Different examination methods of VRP and effects of interobserver variability were evaluated to define a standard operating procedure (SOP) suitable for the specific use in epidemiological studies. Subsequently the feasibility of the SOP was investigated in a larger number of participants.

STUDY DESIGN

Cross-sectional study.

METHODS

In a first phase both the spVRP and the siVRP of 51 female students were measured by four differently experienced examiners. Using a cross-over study design the effects of two different recording methods (manual vs automatic) and three different types of instructions given by the examiner (none vs before vs during recording) were investigated. In a second phase, the SOP for VRP recording was tested in the framework of a feasibility study in 110 (55 female and 55 male) participants.

RESULTS

The average total investigation time was significantly (P = 0.001) higher for the manual recording method (6.1 minutes ± 1.0) in comparison to the automated (5.5 minutes ± 0.7) recording method. The manual recording method led to significantly lower values of minimum frequency (F0min) (P = 0.013) and minimum intensity (SPLmin) (P < 0.001) and higher values of the maximum frequency (F0max) (P = 0.005) of the siVRP. The maximum phonation time, F0max, SPLmax of the siVRP and the frequency and intensity of the shouting voice (Level IV) of the spVRP showed significantly (P < 0.001) higher values when the examiner was allowed to give instructions and advise during the recording. Voice parameters of the siVRP did not show significant associations with the experience of the examiner.

CONCLUSIONS

Standardization of VRP measurements is important to obtain correct and reproducible data in a reasonable examination time. The SOP proposed here proved to be feasible in the setting of an epidemiological study.

Elicitation of Minimum and Maximum Fundamental Frequency and Vocal Intensity: Discrete Half Steps Versus Glissando

PURPOSE

To investigate the effect of elicitation method, either discrete half steps or glissando, on the minimum fundamental frequency, maximum fundamental frequency, minimum vocal intensity, and maximum vocal intensity.

METHOD

Fifty-six healthy-voice participants (28 males and 28 females) ranging from 18 to 25 years of age participated in the study. Each participant performed both the discrete half steps and the glissando procedure. The minimum frequency, maximum frequency, minimum intensity, and maximum intensity values elicited by each task were analyzed. A portion of participants (five males and five females) returned within 3 weeks to repeat the whole procedure to determine test-retest reliability.

RESULT

The results of Pearson's correlation demonstrated all measures were positively significantly correlated. However, the results of paired t tests showed significant difference between elicitation methods, where discrete half steps could elicit maximal vocal performance better than glissando in terms of minimum frequency, maximum frequency, and minimum intensity. Discrete half steps could elicit higher maximum intensity than glissando in males to a greater extent than in females.

CONCLUSION

The difference in performance elicited by the two procedures may be considered acceptable under some situations (eg, time constraint, patient fatigue). In the clinical setting, the clinician should select the appropriate procedure with the consideration of time and assessment purpose.

Voice Range Change After Injection Laryngoplasty for Unilateral Vocal Fold Paralysis

OBJECTIVES

Patients with unilateral vocal fold paralysis (UVFP) caused by nerve injury manifest with voice changes. This study investigated vocal performance measured by voice range profile (VRP) in patients with UVFP and changes in VRP in response to intracordal hyaluronate injection.

METHODS

Eighty-five patients with UVFP were enrolled prospectively, among whom 68 received intracordal hyaluronate injections. The outcome measurements included VRP, acoustic and aerodynamic analyses, peak turn frequency of thyroarytenoid-lateral cricoarytenoid muscle complex (TA-LCA) measured by laryngeal electromyography, and normalized glottal gap area by videolaryngostroboscopy.

RESULTS

The peak turn frequency of the paralyzed TA-LCA showed a modest correlation with max fundamental frequency (F0) and F0 range. Closed-phase normalized glottal gap area showed modest negative correlations with max F0 and F0 semitone range. Regarding conventional acoustic and aerodynamic analyses, the paralyzed TA-LCA peak turn frequency was only correlated with maximal phonation time. Intracordal hyaluronate injection improved VRP performance by increasing max F0, decreasing min F0, increasing F0 range, and increasing semitone range (all P <0.01) with small or medium strength of effect size (Cohen d, 0.39-0.76).

CONCLUSIONS

Change in voice pitch in patients with UVFP can partly predict impairment of neuromuscular functions and glottal gap. VRP provides a more sensitive reflection of the severity of neuromuscular impairment, compared with conventional voice analysis. The validity of VRP is further supported by a robust response to voice improvements following injection laryngoplasty.

Is Acupuncture Efficacious for Treating Phonotraumatic Vocal Pathologies? A Randomized Control Trial

OBJECTIVES

To investigate the effectiveness of acupuncture in treating phonotraumatic vocal fold lesions.

STUDY DESIGN/METHODS

A total of 123 dysphonic individuals with benign vocal pathologies were recruited. They were given either genuine acupuncture (n = 40), sham acupuncture (n = 44), or no treatment (n = 39) for 6 weeks (two 30-minute sessions/wk). The genuine acupuncture group received needles puncturing nine voice-related acupoints for 30 minutes, two times a week for 6 weeks, whereas the sham acupuncture group received blunted needles stimulating the skin surface of the nine acupoints for the same frequency and duration. The no-treatment group did not receive any intervention but attended just the assessment sessions. One-hundred seventeen subjects completed the study (genuine acupuncture = 40; sham acupuncture = 43; and no treatment = 34), but only 84 of them had a complete set of vocal functions and quality of life measures (genuine acupuncture = 29; sham acupuncture = 33; and no-treatment = 22) and 42 of them with a complete set of endoscopic data (genuine acupuncture = 16; sham acupuncture = 15; and no treatment = 11).

RESULTS

Significant improvement in vocal function, as indicated by the maximum fundamental frequency produced, and also perceived quality of life, were found in both the genuine and sham acupuncture groups, but not in the no-treatment group. Structural (morphological) improvements were, however, only noticed in the genuine acupuncture group, which demonstrated a significant reduction in the size of the vocal fold lesions.

CONCLUSIONS

The findings showed that acupuncture of voice-related acupoints could bring about improvement in vocal function and healing of vocal fold lesions.

The softest sound levels of the human voice in normal subjects

Accurate measurement of the softest sound levels of phonation presents technical and methodological challenges. This study aimed at (1) reliably obtaining normative data on sustained softest sound levels for the vowel [a:] at comfortable pitch; (2) comparing the results for different frequency and time weighting methods; and (3) refining the Union of European Phoniatricians' recommendation on allowed background noise levels for scientific and equipment manufacturers' purposes. Eighty healthy untrained participants (40 females, 40 males) were investigated in quiet rooms using a head-mounted microphone and a sound level meter at 30 cm distance. The one-second-equivalent sound levels were more stable and more representative for evaluating the softest sustained phonations than the fast-time-weighted levels. At 30 cm, these levels were in the range of 48-61 dB(C)/41-53 dB(A) for females and 49 - 64 dB(C)/35-53 dB(A) for males (5% to 95% quantile range). These ranges may serve as reference data in evaluating vocal normality. In order to reach a signal-to-noise ratio of at least 10 dB for more than 95% of the normal population, the background noise should be below 25 dB(A) and 38 dB(C), respectively, for the softest phonation measurements at 30 cm distance. For the A-weighting, this is 15 dB lower than the previously recommended value.

Evidence-based clinical voice assessment: a systematic review

PURPOSE

To determine what research evidence exists to support the use of voice measures in the clinical assessment of patients with voice disorders.

METHOD

The American Speech-Language-Hearing Association (ASHA) National Center for Evidence-Based Practice in Communication Disorders staff searched 29 databases for peer-reviewed English-language articles between January 1930 and April 2009 that included key words pertaining to objective and subjective voice measures, voice disorders, and diagnostic accuracy. The identified articles were systematically assessed by an ASHA-appointed committee employing a modification of the critical appraisal of diagnostic evidence rating system.

RESULTS

One hundred articles met the search criteria. The majority of studies investigated acoustic measures (60%) and focused on how well a test method identified the presence or absence of a voice disorder (78%). Only 17 of the 100 articles were judged to contain adequate evidence for the measures studied to be formally considered for inclusion in clinical voice assessment.

CONCLUSION

Results provide evidence for selected acoustic, laryngeal imaging-based, auditory-perceptual, functional, and aerodynamic measures to be used as effective components in a clinical voice evaluation. However, there is clearly a pressing need for further high-quality research to produce sufficient evidence on which to recommend a comprehensive set of methods for a standard clinical voice evaluation.

Características da fonetografia em indivíduos com equilíbrio dentofacial pós-muda vocal

OBJETIVO: caracterizar, por meio de fonetografia, o perfil da extensão vocal em indivíduos sem alterações pós-muda vocal e equilíbrio dentofacial. MÉTODO: participaram deste estudo 15 homens com idades entre 14 e 35 anos com pós-muda vocal. Eles responderam a um questionário específico, e também foram submetidos a uma avaliação antropométrica da face, a avaliação dento-oclusal, o exame fonetografia e também a uma análise da frequência fundamental habitual da voz. RESULTADOS: frequência fundamental mínima: 89Hz ± 3Hz ou 29st ±14st; Frequência fundamental máxima: 665Hz±179Hz ou 63st±5st; Extensão Vocal: 34st±6st; Intensidade mínima: 66 dB ± 3dB; Intensidade máxima: 114dB ± 5dB; Extensão Dinâmica Máxima: 42dB ± 4dB, Área do Fonetograma: 936,4 dB.st ± 258,8 dB.st ou 42,1 cm² ± 11,6 cm²; Frequência Fundamental Habitual para a vogal "a": 111,26 Hz ± 15,24 Hz. CONCLUSÃO: apesar de os estudos nacionais e internacionais apresentados neste trabalho não considerarem a condição dentofacial dos indivíduos, os resultados foram semelhantes.

The use of analogy in speech motor performance

The acoustic correlates of pitch variation were examined in 40 participants who received analogy instructions or explicit instructions that required them to modulate their intonation during speech production. First, using focus group methodology, professional speech-language pathologists were asked to identify analogies that best described minimum pitch variation (monotone), moderate pitch variation (normal intonation), and maximum pitch variation (exaggerated intonation) in speech. The focus group established that an appropriate pitch variation metaphor may be related to imagery of "waves at sea", with minimum pitch variation represented by a flat calm sea, moderate pitch variation represented by a moderate sea, and maximum pitch variation represented by a choppy sea. Forty adult participants without speech impairments were asked to read aloud a standard paragraph using their habitual pitch variation (control condition). They were then allocated randomly to an analogy or an explicit instruction group and were asked to read aloud different paragraphs with minimum, moderate, or maximum pitch variations. Results revealed that acoustic correlates of pitch variation (standard deviation of fundamental frequency, SDF0) were not different for the control condition, or moderate and maximum pitch variation conditions in the two groups. However, the analogy instruction was significantly more effective than the explicit instruction for inducing minimum pitch variation. Analysis of participants in each group who showed higher than normal pitch variation in the control condition (>.5 SD above the group SDF0) revealed that the analogy instruction was more effective than the explicit instruction in the minimum variation condition. It was concluded that analogy instructions may be a useful tool in speech rehabilitation.

Afecções laríngeas, tempos máximos de fonação e capacidade vital em mulheres com disfonia organofuncional

OBJETIVO: verificar e correlacionar os tempos máximos de fonação (TMF) de vogais, a capacidade vital (CV) e os tipos de afecções laríngeas (AL) de mulheres com disfonia organofuncional (DOF). MÉTODO: pesquisa retrospectiva, transversal, exploratória, não experimental, quantitativa, com banco de dados de medidas de TMF [a, i, u], de CV e de AL de mulheres com DOF; e os testes estatísticos Qui- quadrado e exato de Fisher, para verificar as diferenças entre as variáveis e suas relações e o teste binomial, a fim de verificar a significância de proporção ou percentual da análise descritiva, com p<0,05. RESULTADOS: a maioria (22; 75,86%) apresentou TMF significantemente reduzidos (p=0,0053) e sete (24,14%) TMF normais. A CV normal foi estatisticamente significante (p=0,0001) (26; 89,66%), mas três mulheres (10,34%) a apresentaram reduzida. Houve predomínio significante dos nódulos vocais (p=0,0016) (22; 75,86%), seguido de edema de Reinke (6; 20,69%) e de pólipo vocal (1; 3,45%). Dentre as 22 mulheres (75,86%) que mostraram TMF reduzidos, houve predomínio com CV normal (19; 86,36%), embora sem significância estatística (p=0,558). Das mulheres com TMF normais, todas apresentaram CV normal (7; 100%). A maioria com DOF apresentou CV normal, embora sem significância estatística (p=0,199). CONCLUSÃO: nas mulheres com DOF deste estudo, os TMF reduzidos, a CV normal e a presença de nódulos vocais foram significantes e não houve relação entre as variáveis TMF, CV e AL.

Feasibility of measurement of a voice range profile with a semi-occluded vocal tract

Semi-occlusion of the vocal tract may provide a new method for assessing ranges of F(0) and a physiological correlate of vocal intensity. Signals can be obtained without concern about room noise, steadiness in mouth-to-microphone distance, and possibly without vocal injury caused by excessive loudness produced. Nine volunteers participated. Steady and acoustic pressures behind the lips were measured. Traditional voice range profiles were obtained on the vowels /α/ and /u/ for comparison. Range of F(0) was not limited in most subjects with the semi-occlusion but may be restricted in some subjects. In the lower portion of the F(0) range, the highest and lowest steady pressures at the semi-occlusion constitute an oral pressure range profile.

Guidelines for selecting microphones for human voice production research

PURPOSE

This tutorial addresses fundamental characteristics of microphones (frequency response, frequency range, dynamic range, and directionality), which are important for accurate measurements of voice and speech.

METHOD

Technical and voice literature was reviewed and analyzed. The following recommendations on desirable microphone characteristics were formulated: The frequency response of microphones should be flat (i.e., variation of less than 2 dB) within the frequency range between the lowest expected fundamental frequency of voice and the highest spectral component of interest. The equivalent noise level of the microphones is recommended to be at least 15 dB lower than the sound level of the softest phonations. The upper limit of the dynamic range of the microphone should be above the sound level of the loudest phonations. Directional microphones should be placed at the distance that corresponds to their maximally flat frequency response, to avoid the proximity effect; otherwise, they will be unsuitable for spectral and level measurements. Numerical values for these recommendations were derived for the microphone distances of 30 cm and 5 cm.

CONCLUSIONS

The recommendations, while preliminary and in need of further numerical justification, should provide the basis for better accuracy and repeatability of studies on voice and speech production in the future.