On Saturday, October 28, and Sunday, October 29, The Oriana Singers and City Voices will perform Claudio Monteverdi’s Vespers, written in 1610 and considered a masterpiece of the early Baroque period.The Oriana Singers, founded in 1979 by artistic director Bill Chin, is a professional a cappella group of six singers (eight for this concert). They will be joined by City Voices, which is an Oak Park-based amateur community chorus of 30 people started in 2009. In addition, the two groups will be accompanied by a 12-piece chamber orchestra of period instruments.“This piece is something I’ve wanted to do pretty much since The Oriana Singers began almost 45 years ago, but I haven’t had the opportunity until now. It’s a very big project involving soloists [The Oriana Singers], a chorus [City Voices], and instruments from the 1600’s that require specialized players. Some parts call for very fast singing and some parts call for a big sound. Everything together will have more impact,