This study investigates smoothed cepstral peak prominence (CPPS) as a quantitative measure of vocal quality in professional singing. CPPS has been validated for assessing dysphonia and vocal clarity in speech, its effectiveness in analyzing sung tone has not been explored at length. Speech and singing share physiological similarities yet differ in pitch range, resonance, and intensity, therefore the potential of CPPS as a diagnostic or pedagogical tool for singers warrants further study. Prior research (Mendes et al., 2023; Toles et al., 2022; Baker et al., 2024) has shown varied findings, suggesting CPPS may be sensitive to acoustic features such as fundamental frequency and intensity but not always predictive of perceived vocal quality. Building on these findings, this study examines whether CPPS can detect subtle changes in timbre and resonance across repeated performances of the same musical phrase by professional vocalists.Using 30 professional solo recordings of Franz Schubert’s “Ellens Gesang III” (“Ave Maria”), Op. 52, No. 6, D. 839, we extracted three occurrences of a repeated sung phrase per performance using Ultimate Vocal Remover (v. 5.6.0). Recordings were selected for consistent phrasing and acoustic environments. The extracted vocal lines were analyzed with Praat (v. 6.4.35) with the Heller Murray CPPS plugin, with the upper frequency limit increased to 1000 Hz to accommodate singers’ extended range. CPPS values were computed for each phrase, and a repeated-measures ANOVA assessed effects across the song.Results indicated a significant effect of time on CPPS, F(2, 58) = 4.17, p = .02, η² = .13. Post-hoc analyses revealed that CPPS decreased significantly between the beginning and end of the first verse (p = .005) and differed between the end of the first verse and the beginning of the second (p = .037), suggesting measurable acoustic variation consistent with expressive or physiological shifts.These findings demonstrate that CPPS can capture meaningful differences in vocal production across repeated musical phrases, supporting its use as a tool for studying vocal efficiency in singing, with implications for vocal pedagogy, musical performance analysis, and cross-disciplinary research linking speech science and vocal performance.