There were times during the Mormon Tabernacle Choir's Christmas concert dress rehearsal when guest soprano Sissel got a little misty.

"There are a few moments when I'm not singing, and I stand and listen to all these beautiful voices and cry," Sissel said during a Friday news conference in The Church of Jesus Christ of Latter-day Saint's Conference Center. "I am amazed at how the directors — Mack Wilberg and Craig Jessop — can control and guide all these voices."

Sissel, born Sissel Kyrkjebo in Norway, is no stranger to the Mormon Tabernacle Choir. She first appeared with the choir in May 2005 for a broadcast of "Music and the Spoken Word," which honored the 100th anniversary of Norway's independence.

"I had heard of the choir before then," said Sissel. "And I knew many people who have performed with the choir. They always told me, 'If you get a chance to sing with the choir, do it. It is the best choir in the world.' So when I was contacted to sing with the choir for the broadcast, I jumped at the chance because I thought it was going to be a once-in-a-lifetime opportunity. Then I was asked to come back and sing the Christmas concert."

Music director Craig Jessop fell in love with Sissel's voice and demeanor when she appeared with the choir last year. So, he took her aside after the broadcast and asked if she would be interested in coming back this year.

"When I first heard her sing live, I was taken by the sincerity and purity of her voice," said Jessop, who, along with Wilberg, was also at the news conference. "Her voice, like her personality, is disarming and genuine. And we felt she would be the perfect fit in the Christmas concert."

Sissel said she was surprised that the organization is such a tight ship. "They say that this choir is an amateur choir," she said with a little giggle. "But they are not. They are the best-sounding choir I have ever heard."

Throughout her career, Sissel has performed with choirs, orchestras, bands and a variety of artists whose styles range from folk to jazz to rock to punk to hip-hop.

Among those with whom she has appeared onstage are opera icon Placido Domingo, rap star Warren G., Irish troubadours The Chieftains, punk band Sort Sol, Neil Sedaka and Diana Krall.

However, she said Thursday night's dress rehearsal, which was open to the public, was a first — a rehearsal in front of 21,000 people.

"The conference center was filled," she said with another laugh. "I asked how many people were attending, and when they told me, I thought, 'Oh, yes. This is just a dress rehearsal."'

Sissel's arrangements were written out for the choir by her personal arranger, Kjetil Bjerkestrand, who has worked with her for six years. "When I write music for her, I think of ways she can sing freely," Bjerkestrand told the Deseret Morning News. "I feel with her, the less I write the more it becomes.