快猫短视频

Lay-ee-odl-lay-ee-odl-lay-hee-hoo. Forget sleigh bells ringing and carol singing, if there鈥檚 one sound that epitomises the festive season it鈥檚 Julie Andrews in The Sound of Music yodelling her heart out on our TV screens.

OK, so yodelling may not be the most sophisticated of singing styles, but neither is it the easiest to achieve. What鈥檚 more, despite a few brave researchers鈥� efforts to discover how its distinctive sounds are produced, the detailed mechanics remain something of a mystery.

Though yodelling is most often associated with the Alps, and we get the word itself from German, its roots appear to lie well away from Europe. In the 13th century, Marco Polo discovered that Tibetan monks routinely used a form of yodelling to communicate over long distances. Soon after his return to Europe, German and Swiss mountain dwellers began yodelling to each other across alpine valleys. Later, immigrants from Europe took the style to the US, where it morphed into the slower and simpler yodels used by cowboys.

In essence, yodelling involves nothing more complicated than singing a long note that undergoes repeated sharp shifts in pitch. As with all human vocalisation, it is the product of the vocal tract, the most critical component of which is the larynx, or voice box. Attached to the trachea just behind the Adam鈥檚 apple, the larynx is made of various types of cartilage and a single bone called the hyoid. Together they provide a framework for the vocal folds, flaps of mucous membrane attached to muscles either side of the larynx.

Sound is produced when air from the lungs flows through the trachea past the vocal folds and sets them vibrating at anything from 110 to 200 hertz. Contracting the muscles alters the shape, position and tension of the vocal folds, which in turn change the pitch of the resulting sound: the stiffer the vocal folds, the faster they vibrate and the higher the pitch they produce.

Human voices have two distinct ranges in pitch that singers call the 鈥渉ead voice鈥� and the 鈥渃hest voice鈥� depending on the part of the body in which the sound resonates most. There is a marked gap between these two ranges, which is noticed most in inexperienced singers. Opera singers are experts at smoothing over this break, while yodellers accentuate it, says Ingo Titze of the at the University of Iowa.

Understanding the anatomy of our vocal apparatus is a start, but watching it in operation is more of a problem, because normal vocalisation relies on rapid movement of the parts of the larynx. Instead most researchers study the voice by measuring acoustic properties, such as its range of pitch and loudness.

Titze, who is a classically trained singer as well as a physicist, uses a different approach. He made headlines in 1992 with Pavarobotti, a singing robot that he created to accompany him on stage. He created Pavarobotti鈥檚 voice using estimated measurements of the size of singer Luciano Pavarotti鈥檚 larynx, vocal folds and airway, which he plugged into a computer program that models the operation of the human vocal tract.

The vocal tract is essentially no different from any other musical instrument, Titze says. His research has shown that the vocal folds share the same two principal modes of vibration as a guitar. The sound you hear from a guitar comes not just from the vibrating string but also from the vibrations of the soundboard 鈥� the wooden sheet that forms the top of the instrument. In the first mode, the soundboard vibrates in and out as a whole, whereas in the second the left and right halves vibrate out of phase, so that when one side is moving in the opposite side is moving out.

Titze has found that vocal folds vibrate in these two modes 90 per cent of the time. Opera singers and yodellers rely on both vibrational modes to achieve their shifts in pitch, only yodellers shift back and forth more rapidly to emphasise the transition between the two voices rather than disguising them.

While our vocal folds may have a certain amount in common with a guitar, the larynx is a rough sort of music maker. 鈥淎ny instrument maker would reject this as an absolutely lousy instrument,鈥� says Titze. The larynx is too small, too irregular in shape, and the mechanical properties of the vocal fold tissue are far inferior to the materials used in string, brass and woodwind instruments. What makes the difference is control exerted by the brain.

Charles Larson at Northwestern University in Evanston, Illinois, is particularly interested in studying how the human brain controls the muscles of the larynx. Conventional brain imaging techniques don鈥檛 work because they are not good at tracking signals that correspond to rapid movements. So Larson instead attaches electrodes to the larynx muscles to monitor their movements, and studies the signals he picks up for clues to the brain鈥檚 control processes.

While The Sound of Music鈥榮 lonely goatherd can yodel with abandon, what about his charges? Can goats and other animals yodel too? Bioacoustician of the University of St Andrews in the UK says it depends on how strictly you define the term. If yodelling is just a repeated sudden change in pitch 鈥渢here are plenty of animals who do that鈥�, he says, pointing to red deer and elk 鈥� although you might question their musicality. Then there are birds: the avian syrinx is more sophisticated than the human larynx and the most advanced songbirds 鈥� mockingbirds, the brown thrasher, or the mynah 鈥� have comparatively broad repertoires.

鈥淲丑颈濒别 The Sound of Music鈥榮 lonely goatherd can yodel, what about his charges? Can goats yodel too?鈥�

We humans do have one advantage, though. 鈥淪ome birds sing and some birds shriek,鈥� observes Titze, 鈥渂ut humans can choose to do both.鈥� And we can yodel into the bargain.