Study reveals what judges truly listen for in opera singing

Opera has always lived at the crossroads of emotion and discipline. A single performance can shape a singer’s future, opening doors or quietly closing them. In competitions, judges listen closely and assign a single overall score that can influence careers for years. Yet what guides that number has long remained uncertain. Many singers train for decades without fully knowing which parts of their voice matter most when experts listen.

A new scientific study from Japan offers rare clarity. By carefully analyzing opera performances and the scores judges gave them, researchers uncovered which vocal traits most strongly influence competition results. The findings show that two features rise above the rest: vibrato and the singing power ratio, a measure of how well a voice carries through space.

The research was led by Haruka Kondo, a doctoral student at the Graduate School of Media and Governance at Keio University. Kondo is not only a scientist but also a soprano opera singer, giving her a personal connection to the question. “For singers, a competition score can define their career, but what it is the judges are listening for has remained subjective and unclear,” she said. “In our study, we scientifically decoded how different vocal and acoustic factors influence judgment scores in opera singing competitions.”

The study was supervised by Associate Professor Shinya Fujii and included Dr. Sotaro Kondoh, a JSPS Research Fellow at Keio University.

Opera singing is shaped by years of strict training. Singers learn breath control, pitch accuracy, clear pronunciation, and emotional delivery. Judges often describe voices using terms like warmth or brilliance, but those words can feel vague. The research team wanted to know which qualities truly influence final scores.

Ten trained Japanese female opera singers took part in the study. Each performer sang the same classical Italian piece, “Caro mio ben,” under identical recording conditions. Using the same song allowed differences in evaluation to reflect vocal qualities rather than musical interpretation.

Four professional vocal instructors, who were also experienced singers, served as judges. They listened to the recordings in random order. Each judge assigned an overall score out of 100. They also rated six specific vocal traits: vibrato, resonance, timbre, diction, intonation, and expressiveness.

"Our research team examined the recordings using acoustic analysis. We focused on three measurable features. The first was the singing power ratio, or SPR. This value reflects how much sound energy appears in higher frequencies that help a voice travel clearly across a hall. The second was the harmonic to noise ratio, or HNR, which relates to voice clarity. The third was LUFS, a standardized measure of loudness often used in audio production," Fujii told The Brighter Side of News.

By comparing judge scores with these measurements, the researchers aimed to reveal which factors truly shaped professional judgment.

When the results were analyzed, a clear pattern appeared. Among the six vocal traits rated by judges, vibrato stood out as the strongest predictor of overall score. The influence of resonance, diction, expressiveness, timbre, and intonation was far smaller by comparison.

Vibrato refers to the gentle and regular variation in pitch that gives a voice warmth and life. It reflects both physical control and emotional engagement. Singers with stable and expressive vibrato tended to receive higher overall scores from judges.

The acoustic analysis told a similar story. Of the three sound measurements, only the singing power ratio showed a meaningful link to competition results. Performances with a stronger SPR consistently earned higher scores.

SPR is closely related to what singers call the singer’s formant. This feature allows a voice to project above an orchestra without amplification. Even when listeners are unaware of the physics behind it, they often perceive such voices as fuller, brighter, and more confident.

Other measures showed little effect. HNR did not strongly influence scores because trained singers already maintain high vocal clarity. LUFS also showed limited impact. Loudness alone, the researchers found, does not determine artistic quality.

“These findings provide a clearer picture of how judges evaluate performances,” Fujii said. “Our research offers objective insights and powerful new tools for vocal training and education. Beyond that, it also addresses foundational questions of how humans perceive sound and art.”

Opera has always relied on emotion. A performance must move an audience, not just impress them technically. Yet competitions demand ranking, which turns art into numbers. This study helps explain how those numbers form.

Vibrato likely matters because it carries emotion. A well-controlled vibrato signals confidence, musical maturity, and expressive depth. Judges may not consciously calculate it, but their ears respond to it instinctively.

The singing power ratio plays a different role. It shapes how easily a voice reaches listeners. A voice with strong high-frequency energy often sounds more present and commanding, even at the same volume level.

Together, these two elements blend emotion with physical projection. One touches feeling, the other touches perception. When combined, they appear to strongly influence how a performance is judged.

Dr. Kondoh believes the findings could change how singers train. “Imagine a voice lesson where instead of relying solely on the teacher’s perception, students can reliably track specific characteristics of their voice on a screen,” he said.

For students preparing for competitions, the results offer reassurance and direction. Success is not about being louder or forcing expression. Instead, careful control of vibrato and healthy vocal projection matter most.

Teachers may also benefit. While technique remains complex, knowing which elements most strongly affect evaluation can help shape practice goals. Objective feedback tools could one day support traditional listening and guidance.

The study does not suggest ignoring artistry. Opera remains deeply human. But it shows that human judgment often aligns with measurable sound features, even when judges rely only on their ears.

By connecting science with musical tradition, the research helps explain why certain voices stand out, even before words are spoken.

The findings may influence how opera singers train, practice, and prepare for competitions. Vocal educators can use objective tools to track vibrato stability and singing power development. This approach may help students understand progress more clearly and reduce uncertainty during training.

For researchers, the study opens new paths into understanding how people perceive music and performance. Linking emotional response with acoustic structure may benefit studies of speech, hearing, and artistic communication.

Over time, this knowledge could support healthier vocal techniques, reduce injury risk, and improve fairness in performance evaluation. By blending art with science, the research strengthens both.

Research findings are available online in the journal Frontiers in Psychology.

Like these kind of feel good stories? Get The Brighter Side of News' newsletter.