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, more grandeur,” Chin said.Including period instruments makes this concert unusual. “There will be sackbuts, which are earlier versions of the modern trombone and cornetts, which are a cross between a brass instrument and a woodwind instrument and sound like a gentle, muted trumpet,” said Chin. The concert will also include a theorbo, which is like a lute with an extremely long neck that allows for low notes. Violins and other stringed instruments, recorders, and a chamber organ will round out the sound.