Surely you are all familiar with that classic scene in the film The Sound of Music, in which the von Trapp children, led by their governess, Maria, perform a puppet show to "The Lonely Goatherd." C'mon, you all know the lyrics: "High on a hill lived a lonely goatherd..." Maybe it's the distinctive yodeling refrain, but I loved that tune as a kid, and found it impossible not to sing along, to the annoyance of anyone else who happened to be in the room at the time. (Jen-Luc Piquant does the same thing with West Side Story's "America," not that she'd ever admit to it.) Craig Ferguson loved the song enough to have his infamous puppets perform it on The Late Late Show -- or at least recognized its intrinsic kitsch value and place of honor in popular Americana.

Another person who loves the goatherd song is Kerry Christensen, "one of the world's most versatile yodelers" -- and who am I to argue with Wikipedia? I heard him perform several years ago at an Acoustical Society of America conference in Salt Lake City; I showed up out of morbid curiosity -- yodeling? seriously? -- and ended up staying for the entire performance because I enjoyed it so much. (Yeah. You heard me. I enjoyed the yodeling. DON'T JUDGE ME!)

Nobody sets out to become a professional yodeler, but Christensen took a shine to it as a hobby, and it turned into a career. He lives in Provo, Utah, but takes his yodeling act to folk festivals, state fairs, and similar events all over the world, "wherever it's appreciated." Utahans are not very appreciative, it seems: he only performs locally a couple of times a year. It reminds me of an old joke my cabaret singer/songwriter friend Peri used to make: "Q: What's the unlikeliest phrase in the English language? A: 'Is that the banjo player's Porsche?'" Like banjo players and Rodney Dangerfield, yodelers don't get no respect.

And that's too bad. Yodeling is a very old tradition that spans several different cultures. True, the word "yodeling" derives from the German jodeln, meaning "to utter the syllable jo." The type of yodeling most familiar to us can indeed be traced back to the German, Swiss and Austrian regions, where it was used as a communication system between alpine peaks, before finding international success in those old Swiss Miss instant cocoa commercials. Nonetheless, while "the Swiss think they invented yodeling," according to Christensen, he has traced its roots back to Africa.

Apparently Tibetan monks first used a form of yodeling to communicate. Marco Polo brought that knowledge back with him to Western Europe, where it quickly became part of the alpine tradition. The American cowboy yodeling tradition -- yippee-kay-yay, y'all! -- came about because European immigrants brought the vocal style with them to the range. The cowboy yodeling patterns aren't as varied as the European traditions. They tend to be slower and simpler, since they were primarily lullabies to calm the cows at night, and also to soothe the animals during milking.

Yodelling may not be the most sophisticated of singing styles, but neither is it the easiest to achieve. What's more, despite a few brave researchers' efforts to discover how its distinctive sounds are produced, the detailed mechanics remain something of a mystery. Until now, perhaps. Via Improbable Research, we learned about the work of Timothy Ebert Wise, who runs the popular musicology program at the University of Salford in the UK and has published many impressive scholarly papers on the subject of yodeling.

There's one thing you can say for yodeling: acoustically, it's pretty darned distinctive. Human voices have two distinct vocal registers: the "head voice" and the "chest voice." Yodeling essentially involves singing an extended note that rapidly, and repeatedly, shifts in pitch between those two registers -- a skillful technique similar to those employed by professional opera singers, albeit for a very different final sound. Yodeling requires the singer to rapidly switch registers within a few seconds at high volume. Essentially, the voice momentarily breaks. Less practiced yodelers often lapse into falsetto, but skilled singers, like Christensen, can smoothly make the transition between registers without doing so. (See figure at right.)

Or, as Wise puts it in a paper that presents a classification scheme for the various falsetto effects he's studied in popular music:

"The precise moment when the break from modal voice into loft, or vice versa, occurs is the distinguishing feature of the yodel. In fact, it is the only distinguishing feature. This break in register is the sonic event within the flow of the musical line that startles and delights the ear. I call this ‘yodel moment' in the musical flow a yodeleme, a coinage analogous to similar concepts such as phoneme and museme and intended to indicate a primary unit of meaning."

I wrote about the science of yodeling for New Scientist back in December 2007 (subscription required), specifically on the human vocal tract and how it produces that distinctive yodeling sound, highlighting the work of Ingo Titze, a researcher at the National Center for Voice and Speech at the University of Iowa. The most critical component of the vocal tract is the larynx, or voice box. Attached to the trachea just behind the Adam's 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. 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.

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 - 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 yodelers rely on both vibrational modes to achieve their shifts in pitch, only yodelers shift back and forth more rapidly to emphasize the transition between the two voices rather than disguising them.

By the way, Titze, a classically trained singer himself, built a singing computerized "robot" -- basically a stationary body with a computer monitor for a head -- in 1992 that he dubbed "Pavarobotti," modeled after the world-famous tenor's larynx, vocal folds and airways. The robot is still around, and even has its own Facebook page. Here's a video of Titze performing a duet of the famed aria "Nessum Dorma" with Pavarobotti:

The human larynx might be a rough sort of instrument. "Any instrument maker would reject this as an absolutely lousy instrument," Titze told me back in 2007, citing the small size and irregular shape of the larynx as examples, along with the inferior mechanical properties of the vocal folds when compared to the materials used in string, brass and woodwind instruments. But unlike those instruments, human beings have a brain. That's why clever performers like Christensen can be pretty darned inventive; over the years, he's come up with a few new twists on classic yodeling.

Take the time he forgot the words mid-song and resorted to playing the "mouth trumpet": he developed that into a "Louis Armstrong Medley," and he sounds eerily like a trumpet when he performs it. A woman came up to him afterwards and congratulated him on his impressive mouth trumpet, then challenged, "But can you do that and yodel at the same time?"

Christensen's initial reaction was no, he couldn't. The two styles require very different techniques. Yodeling must be loose and totally relaxed to get those smooth transitions between registers, while the mouth trumpet needs to be more pinched off, especially at the lips, which mimic the reed/mouthpiece of the actual instrument. Still, he went back home and practiced for over five hours, and finally managed to come up with a hybrid style he terms the "yodelumpet." He believes he is the only yodeler to sing this way, which is probably a mercy -- it's fascinating as a novelty trick, but one wouldn't exactly call it mellifluous.

[NOTE: Adapted (and updated) from a June 2007 blog post in the Cocktail Party Physics archives.]