Objective Measures as Indicators to Determine the Attainment of Resonant Voice: A Scoping Review

This scoping review aimed to identify and map objective measures that have been used as indicators to determine the attainment of resonant voice (RV).

A systematic search was conducted across four electronic databases (ScienceDirect, PubMed, Web of Science, and Scopus), as well as manual sources and gray literature. Study selection followed the Population-Concept-Context (PCC) framework. Eligible studies included quantitative research involving normophonic or dysphonic individuals and typical or professional voice users across all age groups and genders. Included studies used objective measures related to auditory or tactile feedback to indicate the attainment of RV, within the context of resonant voice therapy (RVT) or its variations.

The review identified ten studies relevant to the research question. Two categories of objective measures were reported, ie, acoustic and vibratory, with acoustic parameters being more frequently studied. Most parameters demonstrated patterns supporting RV, either through directional trends favoring RV over typical voice (TV) or observable differences between the two. Among the acoustic parameters, cepstral peak prominence (CPP) and the 11-point amplitude perturbation quotient (APQ11) demonstrated replicated findings across two studies that favored RV over TV, supporting their potential as reliable indicators. Although reported in individual studies, several other acoustic parameters also showed promise, including fundamental frequency for CPP (CPPF_o), extended perturbation quotient (EPQ), 5-point period perturbation quotient (PPQ5), irregularity, formants (F1 to F4), and formant-harmonic relationships (F1-F_o, F1-H2). As for vibratory parameters, although evidence on root mean square millivolt (RMSmV) was limited to two studies and did not reach statistical significance, both reported greater vibratory amplitude during RV production compared with TV, suggesting potential relevance as an indicator of RV attainment.

Objective measures show potential as indicators of RV attainment. However, evidence remains limited and methodologically varied. Further research is needed to validate these measures and expand their applicability in clinical and technological tools for RVT.