Synthesizing a choir in real-time using Pitch Synchronous Overlap Add (PSOLA)

The paper presents a method to synthesize a choir in real-time and its application in the framework of an opera production. It intentionally integrates artistic considerations with research and engineering matters, thus giving a complete picture of a concrete collaboration in the context of the creation of electronic music. The synthesis of the”virtual choir” is implemented for the jMax real-time sound processing system using the Pitch Synchronous Overlap Add (PSOLA) technique. The synthesis algorithm derives multiple voices of a same group from a single recording of a real choir singer. The first stage of the analysis segments harmonic, non harmonic and transient parts of the signal. The second stage places PSOLA markers in the harmonic parts by a novel two-steps algorithm. The synthesis algorithm allows various transformations of the analysed sound of a single voice by the introduction of stochastic as well as deterministic variations. It is controlled by an extended set of parameters and results in a wide range of different timbres and textures in addition to those of a realistic choir sound. The last section of the paper is dedicated to the application of the algorithm in the context of the composition and its integration into the rest of the environment of the opera production. It describes the experiments with the recordings of a choir and the work in the production studio using the jMax environment. Finally a set of commented examples is associated with the paper, which will be presented during the paper session.