A series of demonstrations of synthesized acappella songs based on an auditory morphing using STRAIGHT [5] will be presented. Singing voice data for morphing were extracted from the RWCmusic database of musical instrument sound. Discussions on a new extension of the morphing procedure to deal with vibrato will be introduced based on the statistical analysis of the database and its effect on synthesized acappella will also be demonstrated. Keywords Rencon, Acappella, RWCdatabase, STRAIGHT, morphing