Opera buffs who look at the subtitles, or text, to understand the words being sung, no longer need to be embarrassed.
Sopranos' voices in the top range make vowels sound the same
A new study has found it's not their hearing that's the problem, but the way sopranos amplify their voices to be heard above the boom of the orchestra.
Australian physicists found that a soprano's ability to sing powerfully in the high part of their vocal range comes at the cost of clarity.
Details of the research have been published in the journal Nature.
Researchers from the University of New South Wales examined how sopranos boost the sounds coming from their vocal cords by adjusting the shape of their vocal tract.
The vocal tract is a fleshy tunnel, including the mouth and tongue, through which sound travels and resonates. It has several resonances that boost or amplify sounds produced in the larynx.
"It's a bit like a megaphone except that we can change the megaphone's shape and different frequencies get amplified," Professor Joe Wolfe, a physicist at the university, told Reuters.
The study measured four specific vowel sounds - "la", "lore", "loo" and "le" - and found that, in the top half of their range, sopranos tuned vocal tract resonances quite accurately to the pitch they were singing.
This makes the voice louder and more uniform, but the vowels end up sounding very similar, explaining why opera is difficult to understand even for those who speak the language in which it is sung.
"It's possibly one reason why opera houses use subtitles even when the words to an opera are in English," Professor Wolfe said.
Joint author Elodie Joliveau, a French soprano and physics honours student, said the effect had not been confirmed before because of the technical difficulty of measuring the acoustics of the vocal tract.
The authors did about 70 measurements of nine sopranos singing the four vowel sounds in a two octave range.
Using technology developed by Wolfe and colleague John Smith for applications in speech therapy, they were able to transmit different frequencies into the singers' mouths while they were singing.
They then measured how the transmitted sound was amplified independently of the frequencies that were present in the voice.