A huddle circle of men, dressed in round black hats and bright red waistcoats, burst into a song of "Yodelayheehoo" in their falsetto voices that echo across the mountain valley. High in the Alps, the resort of Davos is playing host to the Swiss Federal Yodeling Festival, a three-yearly magnet for lovers of mountain folk music and the region's centuries' old traditions.
"It's all in the technique," said 35-year-old Roger Bider, as bystanders applauded his eight-man group's spontaneous performance on a station platform.
"You flip between singing from your head and your diaphragm," said the soft-spoken Bider, one of two yodelers whose fellow singers provided a bass-voice backing.
Known internationally for the annual World Economic Forum gathering of business and political leaders, this is the first time Davos is hosting the four-day yodelling festival.
The national event, which wraps up Sunday and is broadcast live on Swiss television and radio, first began in 1924 and draws 10,000 traditionally clad participants and 100,000 fans.
While the events have juries, it's hardly a battle of the bands: there are no prizes, beyond respect.
"You get hooked," explained Paul Mettler, 62, of the Swiss Yodelling Association, which supervises the event.
- More than music -
Most participants are from Switzerland's majority German-language cantons -- the equivalent of US states -- whose guttural dialects bemuse outsiders.
Traditional Swiss yodel songs include lyrics in dialect but, like folk music worldwide, tell stories of love and hardship.
"When I listen to vintage blues, I hear similar rhythms, harmonies and themes," said Mettler.
Peter Sutter, a yodeler for 30 years, said it was his passion for a host of reasons.
"Culture and tradition are important," said the 59-year-old from the small, central canton of Schwyz, which gave Switzerland its name.
"The key is to be able to sing, to get the idea of sound, rhythm and scales," he added.
Sutter is unimpressed by the "Schlager" pop pumped out in local bars and popular in central Europe, which mixes traditional accordion and yodel sounds with simple electronic beats.
But that's not to say he doesn't appreciate more modern music: "I also like AC/DC, Creedence Clearwater Revival and Deep Purple!"
Other musicians are mixing traditional Alpine music with new sounds.
Sonalp, a group from the cheese-making Etivaz region in western Switzerland, are influenced by rap and world music, using local alphorns, cowbells, accordions and fiddles, along with didjeridoos.
"We meld Swiss folk with other styles. We use yodeling a lot. Our stuff's quite well-received, albeit not by everyone," fiddle-player Guillaume Wahli, 36, told AFP by telephone.
Yodeling is not uniquely Swiss. It is a hallmark of Austria's Tyrol region, and variants are found along central Europe's mountain chains, from Poland to Romania.
"It's been around since we started working the Alps centuries ago. People spent 100 days up there. They couldn't see each other, so they communicated by song," said Mettler.
The patriotic edge came later, said music historian Claude Bonard.
From the early 19th century onwards, Switzerland used music, wrestling and sharp-shooting festivals to forge a united identity in a country of disparate regions.
"It's striking how mass events assembling communities around one ideal continue to this day, bringing together generations to keep age-old traditions alive," Bonard said.
- 'Yoga with a twist' -
The festival also holds recitals featuring alphorns -- a 3.6-metre (12-foot), pipe-shaped instrument -- as well as flag-throwers, who hurl banners aloft and deftly catch them.
In a field, a crowd sat silently on benches listening to an alphorn's mournful tones.
"I'm pretty satisfied," said player Laurent Denervaud after his performance, hoisting his alphorn onto his shoulder.
"The biggest risk's losing track, or dry lips. The jury's watching for tone and musical quality," said the 60-year-old from the mainly French-speaking western canton of Fribourg.
"You need daily practice. In the winter I do it in my garage, but otherwise, I head to the woods," added Denervaud, who has played the alphorn and its smaller cousin the buechel for two decades.
A waiting fellow competitor paced around, blowing raspberries to keep his lips supple.
Musical passion isn't cheap: an alphorn, hand-crafted from spruce, metal and reeds, costs the equivalent of $3,800 (2,800 euros).
"It takes me 55 to 60 hours to make one. You need mountain spruce and the tree-rings have to be tight, ideally from a 400-year-old tree," said Heinz Tschiemer, 31, from the mountains near the capital Bern.
But for committed players, the outlay is worth it.
"Playing keeps you calm and gives you a kind of inner peace. It's like yoga with a twist," said Katrin Christen, 28, who plays in a 10-piece group.