RESUMEN
INTRODUCTION: Vibrato is an oscillation in frequency, intensity, and timbre of the singing voice. Previous studies have found a relationship between its periodicity and perceived quality. The diversity of vibrato enriches the music and singer's performances but create challenges for quantifying and capturing the characteristics that contribute to achieving these expressive goals. Vibrato tones have been addressed using rate, extent, jitter, and shimmer; however, these do not necessarily capture relevant complex time-varying features. This paper applies techniques from disciplines that specialize in periodicity and complexity to provide insight into vibrato characteristics not yet understood. OBJECTIVES: This study aimed to assess whether nonlinear metrics are relevant features in characterizing and illustrating differences in vibrato behavior in opera and jazz singing, as well as considering the relationship of nonlinear metrics to other vibrato parameters. METHODS: Vibrato tones from published music material of world-class singers from opera and jazz were analyzed with entropy, recurrence, and the established parameters of rate, extent, jitter, and shimmer. Dimensionality reduction was employed to consider the relationship and significance of each of the metrics in collectively characterizing vibrato. RESULTS: The principal component, explaining 40% of variability, had positive weights of determinism and line length derived from recurrence while having negative weights of rate, shimmer, and sample entropy. Using these components, the vibrato tones from opera compared to jazz singing were found to be more regular and had lower rate and extent, and it was possible to spotlight singers and notes with high periodicity. CONCLUSION: Our study shows that nonlinear metrics applied to vibrato tones provide a valuable tool for observing and quantifying regularity in vibrato tones. The results of this study highlight the potential for more detailed descriptions of vibrato characteristics that may support categorization of individuals, genres, or musical expression in the future and could be applicable to pedagogical techniques.
RESUMEN
INTRODUCTION: Arguably one of the most controversial features of the singing voice, especially in a choral context, is the phenomenon of vibrato. Numerous pedagogical articles, mostly written by experienced choral singers or directors, discuss the importance of vibrato, sharing anecdotal insights about its control (often advocating reduction) in choral blend and vocal health. OBJECTIVES: This systematic review aims to identify the main questions posed in the empirical study of vibrato during group singing, and how they have been addressed to date through empirical investigations. METHODS: The Preferred Reporting Items for Systematic Reviews and Meta-Analyses was employed for this review. The review team consisted of the two authors. A data extraction form was designed to capture information about the participants (including age, gender, music and singing experience), study methods, experimental procedures, outcome measures, and statistical findings. RESULTS: Seventeen studies were included in the review and revealed that (a) relatively few empirical investigations have studied vibrato in vocal ensembles; (b) the majority focused on vibrato production rather than perception; (c) methodological approaches include Synthesis, Multi-track recordings, Stereo/Binaural recordings, and Lx/Contact recordings; and (d) the studies focused on the main themes of Adjustment, Identification, Interaction, Intonation, and Style. CONCLUSION: With the current body of literature, it is not possible to draw general conclusions around vibrato behavior during group singing. However, the review highlights the main subareas of interest and valuable methods which have been established and through which future research can collectively shed further light on the role of vibrato in choral singing.
