Outside, it is -5C and the quadrangle in front of the 13th century church is like a skating rink. But the fur- wearing Viennese mass-goers and intrepid Japanese tourists delighted to have secured tickets to hear the angelic voices at close range are queuing.
Disappointingly, the boys are concealed from view and the tourists have to crane their necks to catch a glimpse. The atmosphere is only slightly marred when a man enters the chapel afterwards, brandishing CD recordings of the choir.
ELEVEN-YEAR-OLD Reinhard Gabriel, in navy coat and sailor hat, gets ready to go home for Sunday lunch with his father, Helmut. Next year he sets off on a tour covering every major European city, but Mr Gabriel says it's worth it.
"Of course he misses us but even when he's in Vienna we only see him twice a week. And he has the right attitude. He will do it." The family has already made sacrifices for Reinhard by moving from Linz to Vienna.
THE 18TH-CENTURY Augarten Palace, once a Habsburg residence, is now the boarding- school home of the choir. Behind its high walls the gardens and playing fields echo to childish shouts and the soft thud of snowballs hitting woolly coats. Inside the baroque palace, the school principal, Manfred Seipt, sits in his office, wondering where the choir will get its next artistic director from.
The truth is that 500 years after Emperor Maximilian I recruited 12 boys by decree into the royal musical household, this unique institution is in crisis. Its image took a battering three weeks ago when Agnes Grossman, the choir's first female artistic director, said the boys were exhausted, overworked, ruthlessly exploited for commercial profit and being robbed of their childhood.
The claim shocked Vienna, provoking debate about what the choir represents. Linked to such figures as Mozart, Haydn and Schubert (who was in the choir), it has become a symbol of the city's musical heritage. But with no state subsidy since the collapse of the empire in 1918, it has increasingly had to rely on commercial activities.
Miss Grossman, awarded a silver cross by the state for services to the arts, resigned after an internal feud about the length of foreign tours (typically two to three months) and the vulgarisation of the repertoire.
It should not have been like this, on the choir's 500th anniversary. A three-month US tour to overseen by Miss Grossman was an artistic triumph. Music critics, worried about the decline in recent years, hailed the choir's return to its serious musical heritage and original mission. Now all that is in doubt again.
Many parents are unsettled and have taken up Miss Grossman's demands for a reduction in tours and concerts. For years they remained silent but now admit they are heartbroken to see their 10-year-olds disappear on tour for three-and-a-half months of the year.
THE AUGARTEN is in festive mood as Christmas approaches but there is a heavy schedule ahead of the boys in the Haydn choir, who are not on tour (the other three choirs are). Schoolwork has to be compressed into eight-week terms to fit in the travel, but these are gifted boys, the elite of Austria's musical youth.
Lucio Golio, a tutor, is playing part of Mozart's Coronation Mass on a grand piano. Five sopranos, in tracksuits and slippers, study their scores. Lucio makes them repeat a difficult phrase over and over, crying "Bravissimo!" when they get it right. Another group will go to the Vienna Opera House to take part in a performance of Puccini's Tosca tonight. Last night there was a special concert in the baroque salon of the Augarten.
It's not exactly as it was in the days of Schubert. In the recreation area, older boys are huddled over Gameboys. A few more are watching skiing on television. Over the beds in the dormitories, Pamela Anderson and the Spice Girls adorn the walls. "They are normal boys," says Mr Seipt. "We have even caught boys smoking."
But few normal boys get flown to Germany to take part in a Christmas special of the country's most popular television show. Lionel Ritchie is supposed to accompany them, only he is struck down with hoarseness, leaving 20 million viewers disappointed. Instead, the choir sings a jazzed- up version of "Silent Night".
Television shows, CDs and other marketing tools are overseen by the choir's public relations man, Daniel Landau. At the risk of introducing a note of kitsch, the directors have agreed to a new range of merchandise. Vienna Boys Choir T-shirts, pens and paperweights are being tested. The teddy bear in the sailor suit is tipped to be the big seller. There will soon be an Internet site.
ON THURSDAY night the entire Haydn choir flies to the Netherlands for a big charity concert. It is one of the rare moments when there is no choir boy on Viennese soil.
Back in Vienna, Mr Seipt uses the following day to write the speech he will deliver on the night before Christmas Eve when the Bruckner, Mozart and Schubert choirs return from New York and all the boys gather with their parents in the Augarten baroque salon to exchange gifts and sing "Adeste Fidelis".
"So many highs and one very big low" is how he sums up the past year. He will close the door when the boys have gone and think about how to undo the "huge damage" inflicted by Miss Grossman's outburst.
He is keen to keep many of her revolutionary ideas. The stuffy atmosphere and strict rules have been relaxed, the boys go home more often, girls are admitted to the kindergarten and the parents have more rights.
But the record companies and commercial concert organisers have also tied them into long-term obligations. The joyous atmosphere at the New Year's Day concert in the Hofburg will be tinged for many with the knowledge that many homesick months of 1999 have yet to be spent trailing through the concert halls and hotels of the world.