Study explores the vocal qualities and acoustic features that influence how judges score classical singers.
After hearing someone sing, one can instantly judge whether they are "good" or not. But which qualities of the voice help someone judge this and how judges determine the score remains unknown. Now, a new study reveals that in a simulated vocal competition, some of the qualities experts look for include vibrato, resonance, and expressiveness. The findings offer a step toward understanding how experts evaluate classical singing and could help improve vocal training.
Expert listeners can often form an immediate impression of a singer’s performance. But what exactly in the voice drives that judgment? In classical vocal competitions, performers are rated on an overall score. However, the criteria behind that score are rarely made explicit. Moreover, voice quality is often described in vague, metaphorical terms, such as “ringing,” “warm,” or “focused,” which can mean different things to different listeners.
To better understand what lies behind these judgments, a team of researchers led by Assistant Professor Haruka Kondo from Graduate School of Media and Governance, Keio University, Japan, along with Dr. Sotaro Kondoh from the Faculty of Environment and Information Studies, Keio University, and Japan Society for the Promotion of Science, Japan, and Associate Professor Shinya Fujii from the Faculty of Environment and Information Studies, Keio University, Japan, simulated a vocal competition in a concert hall, asking expert judges to evaluate the singers and investigating which vocal attributes and acoustic features were associated with higher overall scores. The study, to be published online in the Journal of Voice on October 27, 2026, provides measurable ways to understand how experts evaluate classical singers.
Assistant Professor Haruka Kondo is a Ph.D. student in vocal science at Keio University and an operatic soprano who has competed in various vocal competitions. She conducted the study with Dr. Sotaro Kondoh, Ph.D., a Japan Society for the Promotion of Science Research Fellow and Visiting Research Fellow in musical meter, beat, and rhythm perception, and Associate Professor Shinya Fujii, Ph.D., who specializes in the neuroscience of music and directs Keio University’s Neurosciences and Music Laboratory. The researchers are affiliated with Keio University’s Research Center for Music Science, which uses scientific approaches to study how music is perceived, understood, created, and experienced, as well as its effects on the brain, mind, and body.
“Our study bridges the gap between artistic intuition and science and does not aim to replace the expert ear. It helps translate what experienced listeners hear into a shared, measurable language,” says Ms. Kondo.
The researchers recruited 22 classical singers, including 10 men and 12 women. Each singer performed the same song, “Caro mio ben,” a cappella, without instrumental accompaniment, in a concert hall to recreate the conditions of a live performance. Five expert judges gave each performance an overall score on a 100-point scale and rated six vocal attributes on a 7-point scale, covering aspects such as pitch variation (vibrato), voice quality (resonance and timbre), clarity of words (diction), pitch accuracy (intonation), and expressiveness.
The participants’ voices were also analyzed for four acoustic features: singing power ratio, which reflects the prominence of certain frequencies in the voice; loudness units relative to full scale, a standardized measure related to perceived loudness; vibrato rate, which describes how quickly the pitch changes during vibrato; and vibrato extent, which describes the amount of pitch change during vibrato. The researchers then examined which vocal attributes and acoustic features were associated with higher overall scores and whether these relationships differed between male and female singers.
Notably, judges gave higher overall scores to singers rated as having better vibrato, resonance, and expressiveness, while timbre, diction, and intonation showed no clear link to scores. Voices with greater spectral prominence in the 2–4 kHz range also tended to receive higher scores in both men and women. This range is linked to the “singer’s formant,” which is thought to give trained voices a clear, ringing quality that helps them carry without a microphone. Higher vocal loudness, however, was not associated with higher scores.
It was observed that judges evaluated male and female singers differently based on their vibrato. Among male singers, a faster vibrato was linked to lower scores, while among female singers, a wider vibrato was linked to higher scores.
“Our results show that something as personal and artistic as ‘a beautiful voice’ can be partly understood through science. This could help students understand what their instructors mean when they say, ‘let it ring more’ or ‘your vibrato is too shallow.’ Students could then use these measurements to see how their voices change as they practice between lessons, which could help organizers design clearer scoring sheets and help singers understand their results,” says Ms. Kondo.
The researchers also see potential for these measures to improve singing-training apps and artificial intelligence voice-evaluation tools that give users feedback that reflects expert judgement.
“In summary, our study paves the way for more efficient and concrete teaching in music education, greater transparency and fairness in competitions and auditions, and designing singing evaluation tools that better reflect how experts listen,” concludes Ms. Kondo.
Title: Vocal evaluation of classical singing in a concert hall
Caption: For classical singers, the qualities of their singing that influence judges’ scores are not always clear. Researchers have now identified measurable vocal features that help explain how experts rate a performance. Notably, judges gave higher overall scores to singers rated higher in vibrato, resonance, and expressiveness, while timbre, diction, and intonation showed no clear link to scores.
Credit: Haruka Kondo from Keio University, Japan
License type: Original content
Usage restrictions: Cannot be reused without permission.
About Haruka Kondo
Haruka Kondo is a Ph.D. student specializing in vocal science at the Graduate School of Media and Governance, Keio University. Alongside her academic pursuits, she is an accomplished operatic soprano and the representative of Opera Lab Japan. She was awarded Third Prize at the 2025 New York International Classical Music Competition.
About Prof. Shinya Fujii
Dr. Shinya Fujii obtained MS and Ph.D. degrees in Human and Environmental Studies from Kyoto University in 2007 and 2010, respectively. He currently serves as an Associate Professor at the Faculty of Environment and Information Studies, Keio University. He is also the Director of the Neurosciences and Music Laboratory at Keio University and the Research Center for Music Science at Keio University Global Research Institute. Dr. Fujii specializes in perception neuroscience and its relationship with music. He has over 75 papers credited to his name.
https://neuromusic.sfc.keio.ac.jp/
https://www.keio.ac.jp/en/org/kgri/research-centers/2026/A26-20/
About Sotaro Kondoh
Sotaro Kondoh, Ph.D., is a JSPS Research Fellow and Visiting Research Fellow at Keio University. His research focuses on musical meter, beat, and rhythm perception. He also investigates music chills, musical interaction, social bonding, and respect-related emotions, employing methodologies such as EEG, heart rate assessment, and psychophysical measurements.
About NeuroMusicLab at Keio SFC
Neurosciences and Music Laboratory at Keio University Shonan Fujisawa Campus
The NeuroMusicLab at Keio SFC is dedicated to research in Neurosciences and Music (NeuroMusic), seeking to understand the fundamental role of music in human life. The research is founded on the premise that music provides a unique probe for identifying higher-order brain functions, including skilled motor control, learning, perception, cognition, memory, emotion, and creativity. The laboratory aims to elucidate the neural origins of human musicality, thereby enhancing the potential of music to contribute to a harmonious future.
While interest in the Neurosciences of Music has surged globally in recent decades, Japan had a notable lack of laboratories in this field. Recognizing the growing need to explore the neural basis of human musicality, Dr. Shinya Fujii founded the NeuroMusicLab at Keio SFC to fill this gap.
About Research Center for Music Science
The Research Center for Music Science (RCMuS) is a research center dedicated to the scientific study of music. Guided by the principle "For the Future of Music, For the Music of the Future, "the RCMuS aims to scientifically elucidate the origins and evolution of music, its universality and diversity, the principles underlying the perception, cognition, generation, and creation of music, the effects of music on the brain, mind, and body of living organisms, and the impact of music on individuals, groups, and society. The center seeks to advance research and education in music science and to disseminate the knowledge gained to the broader public.
https://www.keio.ac.jp/en/org/kgri/research-centers/2026/A26-20/
Funding information
This work was supported by the Taikichiro Mori Memorial Research Fund of Keio University, the Keio University Doctorate Student Grant-in-Aid Program from the Ushioda Memorial Fund, and JST SPRING [grant number JPMJSP2123]; by the Ishii-Ishibashi Fund (Keio University Grant for Early Career Researchers), JST COI-NEXT [grant number JPMJPF2203], JST PRESTO [grant number JPMJPR23S9], and JSPS KAKENHI [grant numbers 24H02199, 23K25750 and 25K21813]; and by JSPS KAKENHI [grant number 24KJ1930].
Reference
Journal： Journal of Voice
DOI： 10.1016/j.jvoice.2026.09.070
Article Title： Vocal Evaluation of Classical Singing in a Concert Hall: Perceptual and Acoustic Associations with Overall Scores in Male and Female Singers