The article describes a flexible mapping technique realized as a many-to-many dynamic mapping matrix. Digital sound generation is typically controlled by a large number of parameters and efficient and flexible mapping is necessary to provide expressive control over the instrument. The proposed modulation matrix technique may be seen as a generic and selfmodifying mapping mechanism integrated in a dynamic interpolation scheme. It is implemented efficiently by taking advantage of its inherent sparse matrix structure. The modulation matrix is used within the Hadron Particle Synthesizer, a complex granular module with 200 synthesis parameters and a simplified performance control structure with 4 expression parameters.