(ISNS) -- For audiences that attend the traditional Christmas performances of Mozart's opera "The Magic Flute," a highlight is the aria "Queen of the Night." But sopranos who must sing the aria often approach the performance with more fear than anticipation.
The challenging solo requires the singer to reach notes more than two and a half octaves above middle C -- an achievement often followed by voice fatigue and the risk of vocal overuse.
Some musicologists have speculated that singers employ a different vocal process when hitting extremely high notes than they do when intoning lower pitches. But a German-Swedish research team using an inventive method of imaging the vocal cords has discredited that theory.
"There is no apparent major difference in voice production at high fundamental frequencies in comparison with lower frequencies," said Matthias Echternach of the Freiburg University Medical Center's Institute of Musicians' Medicine in Germany.
The finding is not entirely surprising. Several experts have cast doubt on the idea of a different means for producing ultra-high notes.
What is significant is the approach that the team used to obtain its result: a flexible fiber-optic tube equipped with a powerful light source and a high-speed camera threaded down through a singer's nose. This high-technology endoscope, as the device is known, enabled the team to capture 20,000 images of a singer's vocal tract each second.
"The project's merit lies in the technology of high-speed imaging," said Ingo Titze, executive director of the National Center for Voice & Speech in Salt Lake City, Utah.
Echternach carried out the research with Freiburg colleagues Louisa Traser and Bernhard Richter, Michael Döllinger of the Erlangen University Medical Center, and Johan Sundberg of the KTH Voice Research Center in Stockholm, Sweden.
Vocal cords, known technically as vocal folds, consist of layers of tissue that produce sound when they vibrate. The faster the vibrations, the higher the pitch of the sound they create. This process, whereby the resistance that the vibrations create to air leaving the lungs leads to the emission of sounds as varied as whispers, shouts, and song, is known as phonation.
Men's vocal folds typically vibrate at rates between 90 and 500 cycles per second, or hertz. For women, the usual range is 150 to 1000 hertz. But to sing such works as the Queen of the Night aria, sopranos must strain to produce vibrations faster than 1050 hertz.
"There are not too many singers who can do the aria with good artistic quality on stage," Echternach said.
The difficulty of singing in such a high register, sometimes called a pipe or whistle register because of the timbre of the notes, led to suggestions that it requires a different process from that used for lower notes.
At those high frequencies, Echternach said, "many people have assumed that the vocal folds are totally stiff and do not vibrate." In that case, the highest-pitched sounds could result from turbulence in the vocal tract.
Checking that assumption requires difficult-to-obtain close-up images of the vocal cords as a singer reaches the highest register.
"Up to now, there were only some studies using low frame rates, employing techniques such as stroboscopy and laryngoscopy," Echternach said. "All have severe problems in analyzing phonation at these high frequencies."
The team's endoscope offered an inventive solution in two ways. It contained the latest in high-speed imaging technology. And the team inserted the device "transnasally" -- that is, through the soprano's nose -- rather than transorally down her throat.
"I would expect that a transoral system would provide 80,000 to 100,000 frames per second, but transoral laryngoscopy is problematic," Echternach said. "Think of singing while you are sticking your tongue out and having a tube inside your mouth. I would suggest that the tensions in the subjects which could be analyzed are not the same as normal."
The comfort factor for the singer as she reached her highest notes more than compensated for the lower frame rate of the transnasal approach.
As their subject, the team relied on a soprano with what they called "a professionally trained voice [that can fill a hall] without the amplification of a microphone."
"Our results clearly show that this professional soprano produced the vocal sound through modulation and interruption of the airflow by the vocal folds up to 1568 hertz, which is in strong disagreement to the theory of a whistle-like mechanism," the team wrote in a paper accepted for publication in the Journal of the Acoustical Society of America.
The team now hopes to confirm its result by testing other sopranos.