(Inside Science) -- Music, for some, is most fully expressed in the form of jazz: distinctive, bent, syncopated improvisation; for others, it is country: patriotic steel twangy ballads; for some it is hip hop: lyrical, sampled, turntable beats; for others still, it is classical: refined, symphonic, orchestral homophony.
And yet there is a whole other subclass of music lovers among us for whom its proper expression is a different beast entirely -- arrogant, angry, aggressive abuse.
They call it heavy metal.
A longstanding mystery has persisted around heavy metal singers for years: How do they do it -- all that screaming, for hours at a time -- and then get off the stage and talk normally? How come they never damage their vocal cords? Now, using high-speed imaging, one San Francisco doctor thinks he found the secret.
Krzysztof Izdebski of the Pacific Voice and Speech Foundation said, "Heavy metal singing is essentially what a baby does."
Not everyone reacts warmly at first to heavy metal singing. Its brazen acoustic effrontery may seem more of a war call than vocal stylings. In fact, some trace its origins to an almost forgotten violent past.
"There is a description by some Arabic merchant who visited northern Europe in [the] ninth century or 10th century, and he says that these people produce sounds that are aggressive, terrible, and … so maybe that’s original heavy metal: a Viking call for submission or whatever it is,” said Izdebski.
But heavy metal singing fascinates Izdebski because he does clinical work with people who have voice problems.
People who injure their throats playing sports and people who use their voices professionally -- actors, teachers -- can strain their voices from too much loud oration, causing the vocal cords to bleed.
"We call it phonotrauma or vocal abuse. And phonotrauma caused by wrong voice usage is something extremely difficult to deal with and it can last for months and months at a time,” said Izdebski.
Yet again there’s the mystery -- how do heavy metal singers scream angry, abusive lyrics for hours with no hint of pathological damage? Using high-tech, high-speed imaging of the throat, Izdebski may have found the answer -- a secret he said babies know instinctively.
"A little baby has all the sounds -- it has the sounds of scream and growl, and inhalation and high pitch and whistle and low pitch, and so I thought, wow, you know, all of this we have, we learn from the beginning. We have it and then we somehow lose it, and the patients who suffer can’t learn how to do this," said Izdebski.
Izdebski's high speed camera can look down someone's throat and record them singing at up to 16,000 frames a second. Using this, combined with sophisticated software, he systematically examined one heavy metal singer in a way that has never been done before.
What you are looking at is slow motion video of one singer's vocal cords. The tissue folds vibrate under an expelled airstream to produce sound. He studied all the sounds this singer could make -- from sucking air to screaming to high whistles to something Izdebski calls the heavy metal growl.
"So a growl is, is one of the most aggressive sounds that heavy metalers do; it sounds something like 'Rahhhh!!!' Okay. So, a growl is produced -- and they can do it over and over and over, hour after hour … The images that we recorded clearly show that it’s produced predominately, predominately by structures above the glottis. So, the vocal folds do open and vibrate but actually don’t collide, and the entire sick area above -- aryepiglottic folds, arachnoids, epiglottis -- everything claps and dances, basically, and creates vibrations and creates acoustic orchestration," said Izdebski.
The analysis appears to have revealed how these singers can sing for hours and still suffer no trauma -- no hint of hyper vascularization, ulceration, bleeding or swelling.
It became clear when watching the videos that the vocal cords never collide -- something you would expect when you raise your voice. And that's the secret. When the air comes up from the lungs and passes through the trachea, over the vocal cords, the structures above the cords tap together – or percuss.
"It’s that the area above [that’s] very loose and the air turbulence that comes through. The air that comes through produces turbulence, and the turbulence produces the sound," said Izdebski.
Izdebski said the work may be relevant to professionals like performers and teachers -- many of whom he sees in his practice. It may also help people who crush their larynxes, a debilitating injury that is common among kids who crash on rails while riding skateboards or adults who suffer clothesline injuries on sail boats.
"When you crush the larynx it cannot be repaired, and these people suffer -- they cannot talk. So, you know, we can use this, this technology -- this artistic technology -- perhaps to try to restore some phonation in these individuals," said Izdebski.
Izdebski plans to continue exploring the clinical applications for this secret technique of heavy metal singers, which he says they do intuitively. Perhaps anyone can learn to do it, since babies are able to do it instinctively. Izdebski also said doing this work has given him newfound respect for the art of heavy metal.
"And these guys do, they do produce really very specific tasks and very specific melodies that are then supported by instruments. And it’s not just kind of going on stage and screaming and doing sort of random stuff. They really compose this stuff," concluded Izdebski.