Purpose: The aim of this study was to investigate voice loudness and gender effects on jitter and shimmer in healthy young adults because previous descriptions have been inconsistent. Method: Fifty-seven healthy adults (28 women, 29 men) aged 20–40 years were included in this cross-sectional single-cohort study. Three phonations of /a/ at soft, medium, and loud individual loudness were recorded and analyzed using PRAAT software (P. Boersma & D. Weeninkk, 2006). Voice loudness and gender effects on measured sound pressure level, fundamental frequency, jitter, and shimmer were assessed through the use of descriptive and inferential (analysis of variance) statistics. Results: Jitter and shimmer significantly increased with decreasing voice loudness, especially in phonations below 75 dB and 80 dB. In soft and medium phonation, men were generally louder and showed significantly less shimmer. However, men had higher jitter measures when phonating softly. Gender differences in jitter and shimmer at medium loudness may be mainly linked to different habitual voice loudness levels. Conclusion: This pragmatic study shows significant voice loudness and gender effects on perturbation. In clinical assessment, requesting phonations above 80 dB at comparable loudness between genders would enhance measurement reliability. However, voice loudness and gender effects in other age groups, in disordered voices, or when a minimal loudness is requested should be further investigated.

In vocally healthy children and adults, speaking voice loudness differences can significantly confound acoustic perturbation measurements. This study examines the effects of voice sound pressure level (SPL) on jitter, shimmer, and harmonics-to-noise ratio (HNR) in adults with voice disorders and a control group with normal vocal status. This is a matched case-control study. We assessed 58 adult female voice patients matched according to approximate age and occupation with 58 vocally healthy women. Diagnoses included vocal fold nodules (n = 39, 67.2%), polyps (n = 5, 8.6%), and muscle tension dysphonia (n = 14, 24.1%). All participants sustained the vowel /a/ at soft, comfortable, and loud phonation levels. Acoustic voice SPL, jitter, shimmer, and HNR were computed using Praat. The effects of loudness condition, voice SPL, pathology, differential diagnosis, age, and professional voice use level on acoustic perturbation measures were assessed using linear mixed models and Wilcoxon signed rank tests. In both patient and normative control groups, increasing voice SPL correlated significantly (P < 0.001) with decreased jitter and shimmer, and increased HNR. Voice pathology and differential diagnosis were not linked to systematically higher jitter and shimmer. HNR levels, however, were statistically higher in the patient group than in the control group at comfortable phonation levels. Professional voice use level had a significant effect (P < 0.05) on jitter, shimmer, and HNR. The clinical value of acoustic jitter, shimmer, and HNR may be limited if speaking voice SPL and professional voice use level effects are not controlled for. Future studies are warranted to investigate whether perturbation measures are useful clinical outcome metrics when controlling for these effects.

This paper reviews recent evidence regarding the validity and reliability of acoustic voice analysis in routine clinical assessments. The current role of jitter and shimmer, the most-used indices, and how their clinical application might be improved are evaluated. Even though the evidence is limited, acoustic analysis is widely used to assist differential diagnosis, documentation and evaluation of treatment for clinical voice disorders. Recent clinical data have not shown that jitter and shimmer are absolute or independent indices of voice pathology or perceptual hoarseness. However, in pretreatment and posttreatment comparisons within patients, acoustic analysis might have value as an outcome measure. Yet, the true value of clinical acoustic analysis might be masked by the confounding effects due to assessment system, gender, vowel and especially speaking voice intensity. The validity of acoustic assessments in clinical applications remains unproven. Measurement reliability is still limited and might be greatly improved with relatively simple changes and consensus in measurement protocols and techniques. For instance, clinical assessment procedures and current normative values would have to be revised considering gender and vowel. Thus, future research might establish the validity and potential of clinical acoustic assessments.

Purpose: Smoothed cepstral peak prominence (CPPS) and harmonics-to-noise ratio (HNR) are acoustic measures related to the periodicity, harmonicity, and noise components of an acoustic signal. To date, there is little evidence about the advantages of CPPS over HNR in voice diagnostics. Recent studies indicate that voice fundamental frequency (F0) and intensity (sound pressure level [SPL]), sample duration (DUR), vowel context (speech vs. sustained phonation), and syllable stress (SS) may influence CPPS and HNR results. The scope of this work was to investigate the effects of voice F0 and SPL, DUR, SS, and token on CPPS and HNR in dysphonic voices. Method: In this retrospective study, 27 Brazilian Portuguese speakers with voice disorders were investigated. Recordings of sustained vowels (SVs) /a:/ and manually extracted vowels (EVs) /a/ from Consensus Auditory-Perceptual Evaluation of Voice sentences were acoustically analyzed with the Praat program. Results: There was a highly significant effect of F0, SPL, and DUR on both CPPS and HNR ( p < .001), whereas SS and vowel context significantly affected CPPS only ( p < .05). Higher SPL, F0, and lower DUR were related to higher CPPS and HNR. SVs moderately-to-highly correlated with EVs for CPPS, whereas HNR had few and moderate correlations. In addition, CPPS and HNR highly correlated in SVs and seven EVs ( p < .05). Conclusion: Speaking prosodic variations of F0, SPL, and DUR influenced both CPPS and HNR measures and led to acoustic differences between sustained and excised vowels, especially in CPPS. Vowel context, prosodic factors, and token type should be controlled for in clinical acoustic voice assessment.