In addition to Cubase VST instruments and the integrated synthesizers (see The Synthesizer) VSampler supports it's own synthesizer plugin-interface. It allows to embed VSampler synthesizers by 3rd party developers into VSampler. You find a demo-synth in the subdirectory /PlugIns together with the respective sources for Microsoft Visual C++ and Borland Delphi 5.0 with the definitions for the synthesizer-interface.
To create your own synthesizer you need to derive the respective class from the base class "VSSynthBase". VSampler synthesizers are Dynamic Link Libraries (DLLs) which reside in the directory /PlugIns. A VSampler synthesizer DLL needs to export the following functions:
The respective functions are described in the example-synthesizer source code.