Minnesota has often been called the choral center of the U.S. The state is filled not only with church and school choirs, but also professional choirs with reputations that extend beyond Minnesota's borders. This is a busy time for many of those choirs as they get ready for their season-opening concerts this month. But missing for the second year is one of the best-known choruses in the state. Minnesota Public Radio's Karl Gehrke has more.