Choir boys' and girls' distinctive voices studied
Even to the untrained ear, it is a magical sound.
Choir boys, and more recently choir girls, have been enchanting congregations for centuries with their distinctive voices.
Some say it is their pure tone, others an angelic shimmer, and then there are those who just cannot put their finger on it at all.
At Ripon Cathedral in Yorkshire, only the very best singers are chosen to form part of the choir.
Edmund Aldhouse, assistant director of music at the cathedral, says: "When we do voice trials and auditions for the choir, one thing that we talk about is that sparkle factor: did the boy or the girl shine.
"And it is just something you know, maybe not something you can define."
But that has not stopped researchers from trying to find out.
Professor David Howard, from the University of York, thinks there is more to the choristers' sound than meets the ear.
Working with music trainer Jenevora Williams, from Guildford, he has been trying to pin down exactly what it is in the singers' voices that make them sound so special.
Professor Howard explains: "The hypothesis is, if we can hear a difference, we should be able to see something that will show us what the acoustic attribute is that means that the brain hears it in that way."
But to study this you need an anechoic chamber - a room designed to prevent any sound from being reflected, which means only the purest tones of volunteer singers are recorded.
Professor Howard uses special software to monitor choristers as they sing.
It breaks this down into the unique set of frequencies that make up their sound.
And he has found that when choir boys and girls sing, particularly soloists, whose voices can soar above the rest of the choir, certain frequencies peak again and again.
He says: "In our experiments it looks as if that particular 'ring' is happening above the normal speech area, in the region up around 8,000 Hz, where there is something appearing when you get this really shimmery sound.
"It's something that makes you sit up, it's something that communicates with the soul. It's way beyond the words, it's way beyond the music, it's something about the content going from the brain of a singer to the brain of a listener."
The frequency peaks, he says, are all down to how the folds within the larynx vibrate, which also explains why a choir boy or girl's voice changes as they approach adolescence and their larynx increases in size.
Previous research has also found that opera singers have a similar resonance - although these appear lower on the frequency spectrum.
Professor Howard says that most choristers produce their sound subconsciously, but quantifying an enigmatic vocal feature to a few squiggles on a graph could help choir boys and girls get more out of their voices.
He says: "The potential may be that it can be used in conjunction with singing training in the studio to help children develop that area of the spectrum, so they develop that certain voice."
And in the future, Professor Howard thinks it could even help scientists to develop a synthetic choir.
He explains: "Maybe you can get to the point where maybe the computer could be at the back of the choir.
"It's a speculative thought, and I think we might get the acoustic right. But what we don't know is the emotional driver - and I think that I think is a long long way off."