OAKLAND, Calif. (KGO) -- If you thought you heard the songs of angels in the air near Oakland's Lake Merritt, those were actually the songs of more than 600 children and teenagers who've traveled to Oakland for an international choir competition.When Robert Geary conducts hundreds of children in song it's more than just music."This festival evokes an emotional response in me that I find overwhelming and I think it is optimism and promise of youth," said Robert Geary, director of the Golden Gate International Choral Festival They come from all over, New York, China and Canada."When we heard them rehearsing for the first time, it's like angels singing. And you can't tell what choir is from where, and everyone just sounds so unified," said Amanda Boger, Alaska Children's Choir director.Such incredible teamwork, it might be surprising that they're here for a competition."It's the only one of its kind in the United States. The kids have been practicing for this for at least a year," Geary said.One group traveled here from Indonesia. "The weather is different. Well, it's quite chilly here," said Antonio Krisanto, a 13-year-old singer from Indonesia.Unless you're from Alaska."It's really warm. We're not used to it," said an Alaskan singer.One of their songs is in Portugese. The Indoneisans have a song in a local dialect.For these kids and teens, it's about so much more than just the notes they're singing. Already, many of them have begun to make friends with people from different countries on different continents, all of them with one language in common -- music."It's cool to just be like so different but be connected all by music," said Grace Hitchen of the Marin Girl's Choir.It's the good and the awkward."I used to sing soprano, but now my voice is cracking," Krisanto said.But whether they wind up as tenors or baritones, some will go on to careers in music and some won't."I kind of want to work for NASA and be an astronaut, so I could sing in space," Hitchen added.