|Abstract||Computer generated singing choir synthesis can be achieved by two means clone transformation of a single voice or concatenation of real choir recording snippets. As of today, the synthesis quality for these two methods lack of naturalness and intelligibility respectively. Unisong is a new concatenation based choir singing synthesizer able to generate a high quality synthetic performance out of the score and lyrics specified by the user. This article describes all actions and techniques that take place in the process of virtual synthesis generation choir recording scripts design and realization, human supervised automatic segmentation of the recordings, creation of samples database, and sample acquiring, transformation and concatenation. The synthesizer will be demonstrated with a song sample.